** Guide to administering Linux on RHEL, CentOS, Amazon AMI's **
Copyright 2014 Craig H
Licensed under the Apache License, Version 2.0 (the 'License');
you may not use this file except in compliance with the License.
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http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an 'AS IS' BASIS,
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See the License for the specific language governing permissions and
limitations under the License.
-
6 Levels to booting
- BIOS
- MBR
- GRUB
- Kernel
- Init
- Runlevel
-
BIOS
- Searches, loads, and executes the boot loader program.
- It looks for boot loader in floppy, cd-rom, or hard drive. You can press a key (typically F12 of F2, but it depends on your system) during the BIOS startup to change the boot sequence.
- Once the boot loader program is detected and loaded into the memory, BIOS gives the control to it.
- So, in simple terms BIOS loads and executes the MBR boot loader.
-
MBR
- It is located in the 1st sector of the bootable disk. Typically /dev/hda, or /dev/sda
- MBR is less than 512 bytes in size. This has three components 1) primary boot loader info in 1st 446 bytes 2) partition table info in next 64 bytes 3) mbr validation check in last 2 bytes.
- It contains information about GRUB (or LILO in old systems).
- So, in simple terms MBR loads and executes the GRUB boot loader.
-
GRUB
If you have multiple kernel images installed on your system, you can choose which one to be executed.
GRUB displays a splash screen, waits for few seconds, if you don’t enter anything, it loads the default kernel image as specified in the grub configuration file.
GRUB has the knowledge of the filesystem (the older Linux loader LILO didn’t understand filesystem).
Grub configuration file is /boot/grub/grub.conf (/etc/grub.conf is a link to this). The following is sample grub.conf of CentOS.
boot=/dev/sda
default=0
timeout=5
splashimage=(hd0,0)/boot/grub/splash.xpm.gz
hiddenmenu
title CentOS (2.6.18-194.el5PAE)
root (hd0,0)
kernel /boot/vmlinuz-2.6.18-194.el5PAE ro root=LABEL=/
initrd /boot/initrd-2.6.18-194.el5PAE.img</strong></span>
As you notice from the above info, it contains kernel and initrd image.
So, in simple terms GRUB just loads and executes Kernel and initrd images.
-
Kernel
- Mounts the root file system as specified in the “root=” in grub.conf
- Kernel executes the /sbin/init program
- Since init was the 1st program to be executed by Linux Kernel, it has the process id (PID) of 1. Do a ‘ps -ef | grep init’ and check the pid.
- initrd stands for Initial RAM Disk.
- initrd is used by kernel as temporary root file system until kernel is booted and the real root file system is mounted. It also contains necessary drivers compiled inside, which helps it to access the hard drive partitions, and other hardware.
-
Init
Looks at the /etc/inittab file to decide the Linux run level.
Following are the available run levels
0 – halt
1 – Single user mode
2 – Multiuser, without NFS
3 – Full multiuser mode
4 – unused
5 – X11
6 – reboot
Init identifies the default initlevel from /etc/inittab and uses that to load all appropriate program.
Execute ‘grep initdefault /etc/inittab’ on your system to identify the default run level
If you want to get into trouble, you can set the default run level to 0 or 6. Since you know what 0 and 6 means, probably you might not do that.
Typically you would set the default run level to either 3 or 5.
- Runlevel
Depending on your default init level setting, the system will execute the programs from one of the following directories.
Run level 0 – /etc/rc.d/rc0.d/
Run level 1 – /etc/rc.d/rc1.d/
Run level 2 – /etc/rc.d/rc2.d/
Run level 3 – /etc/rc.d/rc3.d/
Run level 4 – /etc/rc.d/rc4.d/
Run level 5 – /etc/rc.d/rc5.d/
Run level 6 – /etc/rc.d/rc6.d/
Please note that there are also symbolic links available for these directory under /etc directly. So, /etc/rc0.d is linked to /etc/rc.d/rc0.d.
Under the /etc/rc.d/rc*.d/ directories, you would see programs that start with S and K.
Programs starts with S are used during startup. S for startup.
Programs starts with K are used during shutdown. K for kill.
There are numbers right next to S and K in the program names. Those are the sequence number in which the programs should be started or killed.
For example, S12syslog is to start the syslog deamon, which has the sequence number of 12. S80sendmail is to start the sendmail daemon, which has the sequence number of 80. So, syslog program will be started before sendmail.
- Shutdown the system after 10 minutes.
shutdown -h +10
-
Process States
Init process is the first process when linux boots up
pidof systemd >1There are 4 states for a process
- Running: running or waiting to be assigned to CPU - Waiting: : iowait - waiting for io, or just waiting for an event to occur. uninterruptible are ones waiting on hardware - Zombie: process is dead but its still in process tableBackground Jobs
& or ctrl+zForeground Jobs
jobs fg %1 -
Signals
Signals notify an process of an event. Similar to how a hardware sends kernel interupts. Programs only recognize signals if they are programmed to do so.
Shows all available signals
kill -lSignal Types:
SIGINT - interupprt SIGHUP - when controlling terminal is closed without closing. The OS sends sighup SIGINIT2 - sent when user hits control+c SIGQUIT - sent when quit signal Ctrl + D SIGKIll9 - terminates immediately and without out cleaning up SIGTERM15 - kill uses this by default. Clean shutdown. SIGTSTP2- - Control z -
System Calls
When a program does open, fork, read, write its doing a system call. Its how a program enters the kernel. it instructs the kernel to do something on its behalf. Why doesn’t the user application run itself? Because of ring levels. Users are ring3, kernel is ring0.
Userspace and Kernel space Processes in user space only have access to small part of memory. Kernel has all. Cannot do io or have a hardware access. Access to kernel space by system calls. Sends an interupt to kernel if it wasn’t to write a file. Rings are so programs dont interfere with eachother
- Become system administrator:
sudo -s
sudo su
The accounts capable of using sudo are specified in /etc/sudoers, which is edited with the visudo utility. By default, relevant logs are written to /var/log/secure.
- Switch user
su - user2
argument "-" Provides an environment similar to what the user would expect had the user logged in directly.
- Password file syntax
/etc/passwd
* Username: It is used when user logs in. It should be between 1 and 32 characters in length.
* Password: An x character indicates that encrypted password is stored in /etc/shadow file.
* User ID (UID): Each user must be assigned a user ID (UID). UID 0 (zero) is reserved for root and UIDs 1-99 are reserved for other predefined accounts. Further UID 100-999 are reserved by system for administrative and system accounts/groups.
* Group ID (GID): The primary group ID (stored in /etc/group file)
* User ID Info: The comment field. It allow you to add extra information about the users such as user's full name, phone number etc. This field use by finger command.
* Home directory: The absolute path to the directory the user will be in when they log in. If this directory does not exists then users directory becomes /
* Command/shell: The absolute path of a command or shell (/bin/bash). Typically, this is a shell. Please note that it does not have to be a shell.
-
System User vs Normal User
System users will be created with no aging information in /etc/shadow, and their numeric identifiers are chosen in the SYS_UID_MIN–SYS_UID_MAX range, defined in /etc/login.defs, instead of UID_MIN–UID_MAX (and their GID counterparts for the creation of groups).On CentOS: Although useradd --system foouser creates no home directory for that user. Service accounts often don't have a "proper" login shell, i.e. they have /usr/sbin/nologin. Moreover, service accounts are typically locked, i.e. it is not possible to login (for traditional /etc/passwd and /etc/shadow this can be achieved by setting the password hash to arbitrary values such as * or x) -
Change password
passwd
- Change password expiration
chage
chage -E never username (sets to never expire)
- Lock user password
usermod -L username
- Define default attributes for new users (UID, Password Expiriny, HomeDir)
nano /etc/login.defs
-
Kill a process
1 HUP (hang up) 2 INT (interrupt) 3 QUIT (quit) 6 ABRT (abort) 9 KILL (non-catchable, non-ignorable kill) Each process is supplied with a set of standard signal handlers by the operating system in order to deal with incoming signals. When no signal is explicitly included in the command, signal 15, named SIGTERM, is sent by default. If this fails, the stronger signal 9, called SIGKILL -
Kill all users processes
killall -u username
- Kill all processes by name
killall firefox
pkill -9 firefox
- Get process id
pgrep bash
- Reload process
sudo kill -HUP pid_of_apache
- Display users using file/folder
fuser -u file/folder
- Kill processes using file/folder
fuser -k file/folder
- Add User
add user user1
- Show last logged in
last
last Log
last reboot # shows last reboot
- Show users groups
groups {username}
- Add User to Sudo
usermod -a -G sudo user1
- Change default sudo timeout (in minutes)
add to /etc/sudoers
Defaults timestamp_timeout=<value>
-
Edit Group Config
Nano /etc/groupcdrom:x:24:vivek,student13,raj Where, group_name: It is the name of group. If you run ls -l command, you will see this name printed in the group field. Password: Generally password is not used, hence it is empty/blank. It can store encrypted password. This is useful to implement privileged groups. Group ID (GID): Each user must be assigned a group ID. You can see this number in your /etc/passwd file. Group List: It is a list of user names of users who are members of the group. The user names, must be separated by commas. -
Variables
echo $PATH #shows path variable
export -p #shows all defined
export MYAPP=1 #sets variable my app to value 1
EDITOR="nano"
- Add path to system path
export PATH=$PATH:/usr/local/bin
- Print usernames of logged in users:
users
- Write one line to another user from your terminal:
talk
- show info on current user
id
- show all users and host where logged in from
who -umH
- To temporarily prevent logins system wide (for all users but root) use nologin. The message in nologin will be displayed (might not work with ssh pre-shared keys).
echo "Sorry no login now" > /etc/nologin
- Print full date and time:
date
- Print the hostname of this machine:
echo $HOSTNAME
- Print the default file permissions(subtract from 777):
echo $umask
- Print the session timeout:
echo $tmout
- Print information about current linux distro:
lsb_release -a
cat /etc/*-release
cat /proc/version
- Print linux kernel version:
uname -a
- Print information about kernel modules:
lsmod
- Configure kernel modules (never do this):
modprobe
- Look for messages from drivers:
dmesg
- View Installed packages:
dpkg --get-selections
- Print environment variables:
printenv
- List hardware connected via PCI ports:
lspci
- List hardware connected via USB ports:
lsusb
- Print hardware info stored in BIOS:
dmidecode
sysreport
- Dump captured data off of wireless card:
dumpcap
- Dump info about keyboard drivers:
dumpkeys
- Print information about ethernet
ethtool
- Make a bootable USB
dd if=efidisk.img of=/dev/usb (usb device name)
- Make a swap file
dd if=/dev/zero of=/opt/myswap bs=1024 count=4
mkswap /opt/myswap
swapon -a
For adding this myswap at boot time, add following in /etc/fstab file:
/opt/myswap swap swap defaults 0 0
- Show default kernel
grubby –default-kernel
- Modify kernel parameters
nano /etc/sysctl.conf
- Backup & Restore MBR
To backup: dd if=/dev/sda of=/tmp/mbr.img_backup bs=512 count=1
To restore: dd if=/tmp/mbr.img of=/dev/sda bs=512 count=1
The MBR is a 512 byte segment on the very first sector of your hard drive composed of three parts: 1) the boot code which is 446 bytes long, 2) the partiton table which is 64 bytes long, and 3) the boot code signature which is 2 bytes long.
- Sync NTP time
sudo service ntp stop
sudo ntpdate -s time.nist.gov
sudo service ntp start
- Show Memory information
cat /proc/meminfo
- Show number of cores
lscpu
- Hardware Info
cat /proc/cpuinfo # CPU model
cat /proc/meminfo # Hardware memory
grep MemTotal /proc/meminfo # Display the physical memory
watch -n1 'cat /proc/interrupts' # Watch changeable interrupts continuously
free -m # Used and free memory (-m for MB)
cat /proc/devices # Configured devices
lspci -tv # Show PCI devices
lsusb -tv # Show USB devices
lshal # Show a list of all devices with their properties
dmidecode # Show DMI/SMBIOS: hw info from the BIOS
- Linux file system description:
http://www.tldp.org/LDP/Linux-Filesystem-Hierarchy/html/
- inodes
An inode stores basic information about a regular file, directory, or other file system object
iNode number also called as index number, it consists following attributes:
File type (executable, block special etc)
Permissions (read, write etc)
Owner
Group
File Size
File access, change and modification time (remember UNIX or Linux never stores file creation
time, this is favorite question asked in UNIX/Linux sys admin job interview)
File deletion time
Number of links (soft/hard)
Extended attribute such as append only or no one can delete file including root user
(immutability)
Access Control List (ACLs)
- Show inodes of files and folders
ls -i
stat
- Find where a commmand is executed from
which
ie: which python > /usr/bin
- list directories and recurse into subdirectories
ls -r
- Find files bigger than 100m
find . -size +100M
- Find largest directories in current directory
du -hs */ | sort -hr | head
- Find files created within last 7 days
find . -mtime -7
- Find files accessed within last 7 days
find . -atime -7
- Find Disk Usage by Directory
du -sh /home/*
#Using the -c option with the du command will show the grand total of used space for the designated directory
- check for bad blocks
sudo badblocks -s /dev/sda
- Read speed test
sudo hdparm -tT /dev/sda
- Write speed test. 16KB random write operations
fio --directory=/media/p_iops_vol0 --name fio_test_file --direct=1 --rw=randwrite --bs=16k --size=1G --numjobs=16 --time_based --runtime=180 --group_reporting --norandommap
- Display mountpounts
lsblk
findmnt #show mountpoints
sudo fdisk -l
df -h
df -h --output=source,target
- Add a new EBS disk to server
lsblk #find drive which is not mounted
sudo mkfs -t ext4 /dev/xvdf #makes file system on /dev/xvdf)
(or sudo mkfs -it xfs /dev/xvdf #makes file system on /dev/xvdf)
sudo mkdir /mnt/my-data #make a mount point
sudo mount /dev/xvdf /mnt/my-data #mount device
- Show Physical Volumes
pvdisplay
-
Create Volume Group
A group of physical volumes or disks are combined together into a single storage file which is referred to as the LVM volume group.
sudo vgcreate <volume-name> <device-1> <device-2> <device-3>
- Create Logical Volumes
sudo lvcreate –name <logical-volume-name> –size <size-of-volume> <volume-group-name>
- Display Logical Volumes
sudo lvdisplay
- Format Logical Volume
mkfs -t ext4 /dev/<lvm-name>
- Zero Out all blocks for performance
if=/dev/zero of=/dev/xvdf bs=1M
- Create Raid0
mdadm --create --verbose /dev/md0 --level=stripe --raid- devices=number_of_volumes device_name1 device_name2
- Resize Filesystem
resize2fs
- Raid Levels
0 - Striped set without parity or Striping
1 - Mirrored set without parity or Mirroring
0+1 - (increased speed) arrays are created and they are each mirrored via an overall RAID 1 (data backup) array. By definition, this configuration requires at least 4 drives.
5 - Provides both backup and increased speed. Additionally, a RAID 5 array can continue normally operating if one of its drives fails. The performance speed of the array will be reduced until the failed drive is replaced, but no data loss would occur. This array requires a minimum of 3 drives.
1+0 Mirrors two drives together and then creates a striped set with the pair.
- Mount a new file system
fdisk /dev/hda1 #create new partision
mkfs /dev/hda1 #create file system
mount -a # causes all filesystems mentioned in fstab to be mounted
- Define boot disk
cat /etc/fstab
# UUID=9246707a-30ab-47be-b78f-bb7b24a459a8 / ext4 defaults 1 1
# ext4= filesystem , defaults = mount on boot
- Copy Files from Remote Machine to Local Machine
scp root@www.server.com:/root/file.sql /home/ec2-user
- Copy Local directory to remote machine
scp -rp sourcedirectory user@dest:/path
- Copy Remote directory to local path
scp -r user@your.server.example.com:/path/to/foo /home/user/Desktop/
- Copy hello.txt from local computer to remote home directory
scp hello.txt awshost1:~/
- Copy hello.txt from local to remote home directory, renaming it foo.txt
scp hello.txt awshost1:~/foo.txt
- Copying ~/foo.txt from the remote computer to the current local director
scp awshost1:~/foo.txt .
- Copying ~/foo.txt from remote to local directory cc, renaming it a.b
scp awshost1:~/foo.txt cc/a.b
- Compress a directory
tar -zcvf archive-name.tar.gz directory-name
-c = create
-f = following is archive name
-v = verbose
-z = gzip
- To append file to archive
tar rvf archive_name.tar new file.txt
- Encrypt a file:
gpg -o [outputfilename.gpg] -c [target file]
- Decrypt a file:
gpg -o [outputfilename] -d [target.gpg]
- Uncompress file
unzip filename.zip
- Open a compressed .tgz or .tar.gz file:
tar -xvf [target.tgz]
tar -xvf —strip-components 1 # extracts without its parent folder
tar -xvf -C # extracts to a different directory
- Find Files
Find . -name http*
- Find all files not owned by root:
find . \! -user root -print
- Find all files not with permissions 644:
find . \! -perm 644 root -print
- Find files matching [filename]:
locate [filename]
- Show a file type
file image.jpg
- Show uncommented items in config files
grep -v "#" file.conf
- Search for a given string in all files recursively
grep -r "ramesh" *
- View the differences between two files:
diff [file 1] [file 2]
- Change File Permissions
chmod 775 filename
chmod o+r file.txt # o=other +=add r=read
7 = Read + Write + Execute
6 = Read + Write
5 = Read + Execute
4 = Read
3 = Write + Execute
2 = Write
1 = Execute
0 = All access denied
First number is for the owner, second for the group, and third for everyon
http://permissions-calculator.org/
- Permissions On Folders
r: read only the names of the files in the directory
w: create and delete of the files in the directory
x: traverse the directory
- Permissions On files
r: open a file for reading (e.g. with the cat command)
w: write a file (e.g. use sed -i (inplace) on it)
x: execute a file
It is important to note that a script can be executed even by a user who doesn’t have the execute permission on it. Passing a python script path to the python executable will cause python to open the file for reading and then interpret it. So it is not safe to rely on the executable permission for security. This goes for php, perl, ruby, javascript, etc, etc
- Copy permissions of one file onto another
getfacl FILE1 | setfacl –set-file=- FILE2
- Show permissions on all directories in a tree
namei -om /var/www/iddb.com/static
- Remove directory
rmdir directory
- Logs
auth.log Authentication logs
boot.log Boot logs
btmp Invalid login attempts
cron Cron logs
daemon.log Logs for specific services (daemons)
dmesg Kernel boot messages
httpd/ Apache logs
kern.log Kernel logs
mail* Mail server logs
messages General/all logs
mysql* MySQL logs
secure Security/authentication logs
syslog All system logs
wtmp User logins and logouts
- Check Logs
less /var/log/messages
less /var/log/secure
less /var/log/auth
- Check disk space
df -H # H is for human readable
- Config Files
/etc/login.def - default settings template for new user accounts
/etc/motd - message of the day
/etc/inittab - defines default runlevel #id:3:initdefault:
- System Startup Files
/etc/rc.d - scripts run from this subdir
/etc/init.d - hard location for startup scripts. Linked to /etc/rc.d/rc0.d ..etc.
/etc/rc.d/rc - file responsible for starting stopping services
/etc/rc0.d - contains files with links to /etc/init.d/.
k05atd - kill,priority,service
s05atd - start,priority.service
- To start any script
run /etc/init.d/smb start
# To prevent startup delete sum link
- To create new startup script
put script in /etc/init.d/myservice
/etc/rc3.d ln s ../init.d/myservice
- Check for systemd or sysvinit
pidof /sbin/init && echo "sysvinit" || echo "other"
pidof systemd && echo "systemd" || echo "other"
- Show Current Runlevel
runlevel
who -r
- Change default runlevel
nano /etc/inittab. change id:3:initdefault. to different number
- Change runlevel
init 1 (single user mode)
- Check file system consistency
Goto single user mode:
# init 1
Unmount file system:
# umount /dev/sdb1
Now run fsck command:
# fsck /dev/sdb1
- Check a files type
file <filename>
- Generate md5
md5 <filename>
- Generate sha256
openssl sha -sha256 <filename> (mac)
- Symbolic Links
┌── ln(1) link, ln -- make links
│ ┌── Create a symbolic link.
│ │ ┌── the path to the intended symlink
│ │ │ can use . or ~ or other relative paths
│ │ ┌─────┴────────┐
ln -s /path/to/original /path/to/symlink
└───────┬───────┘
└── the path to the original file/folder
can use . or ~ or other relative paths
- Change the open files limit from 1024 to 10240 d
ulimit -n 10240 # This is only valid within the shell
-
Login users and applications can be configured in /etc/security/limits.conf
-
System wide limits
sysctl -a # View all system limits
sysctl fs.file-max # View max open files limit
sysctl fs.file-max=102400 # Change max open files limit
echo "1024 50000" > /proc/sys/net/ipv4/ip_local_port_range # port range
cat /etc/sysctl.conf
fs.file-max=102400 # Permanent entry in sysctl.conf
cat /proc/sys/fs/file-nr # How many file descriptors are in use
- Find opened files on a mount point with fuser
fuser -m /home
-
Load Average
The "number of cores = max load" The three numbers represent averages over progressively longer periods of time (one, five, and fifteen minute averages) Rule of Thumb: on a multicore system, your load should not exceed the number of cores available. On a dual-core CPU, I won't even think about it until load gets and stays above 1.7 or so Which average should I be observing? One, five, or 15 minute?, you should be looking at the five or 15-minute averages. Frankly, if your box spikes above 1.0 on the one-minute average, you're still fine. It's when the 15-minute average goes north of 1.0 and stays there that you need to snap to. how do I know how many cores my system has? grep 'model name' /proc/cpuinfo | wc -l -
Show running services with their ports
lsof -i # monitors network connections in real time (mac/linux)
- Show what files a process has open
lsof -p $PID
netstat -lptu
-
top
uppercase M sorts by memory
lowercase c shows full command
* check i/o wait for server slowness - Represents CPU waiting for disk I/O. if it is low then you can rule out disk access. GT > 10% is high means Disk is slow
* CPU idle. higher the number the more bandwidth available to server. Should be >25%
* User Time - if idle time is low, you can expect this to be high. Find process taking up cpu
* Memory usage: don't look at the "free" memory -- it's misleading. To get the actual memory available, subtract the "cached" memory from the "used" memory. This is because Linux caches things liberally, and often the memory can be freed up when it's needed
* Stealtime = virtual machines are competing for resources. If %st increases on all VM's, means your VM is using too much cpu. elif %st increases on just one VM = Physical is oversold
* cpu: usertime (time spent on processor running your program). System is the time spent in operating system kernel
* iowait: time cpu waiting for disk or network io.
* load: is how many processes are waiting to run
- < 0.7 = healthy (on single core machine)
- 1.0 = system is fully used (on single core machine)
- 1.0 on single core, 4.0 on quad core
- broken down by one minute, 5 minutes, 15 minutes
- lscpu: shows how many cores
* Memory: true memory usage is memory used - swap cached
* swap: cached: caches files in the filesystem in memory for better performance. Uses spare memory
* SwapTotal, SwapFree. If they are equal there is no swapping going on
- Show open tcp sockets
lsof -nPi tcp
-n : This option inhibits the conversion of network numbers to host names for network files.
Inhibiting conversion may make lsof run faster. It is also useful when host name lookup is not
working properly.
-P : This option inhibits the conversion of port numbers to port names for network files. Inhibiting
the conversion may make lsof run a little faster. It is also useful when port name lookup is
not working properly.
-i [tcp] : This option selects the listing of files any of whose Internet address matches the address
specified in i.
- Show bandwidth usage per connection
iftop
- Show which apps are using the connection
ss -p
- Show Ports listening with thir process id
netstat -tlnp (show ports listening with their process id)
-l, --listening : Show only listening sockets. (These are omitted by default.)
-n, --numeric : Show numerical addresses instead of trying to determine symbolic host, port or user names.
-p, --program : Show the PID and name of the program to which each socket belongs.
-t, --tcp : Show only tcp
- Show Ports listening - Mac only
nettop
- Show bandwith ussage per process
nethogs
- Show running services
ps –ax
ps –eaf
pstree
ps aux
a = show processes for all users
u = display the process's user/owner
x = also show processes not attached to a terminal
- Like top, but with a better, cleaner interface:
htop
- Stop a process from using all system resources and lagging computer:
nice [process name]
nice command is used for changing priority of the jobs.
Syntax: nice [OPTION] [COMMAND [ARG]…]
Range of priority goes from -20 (highest priority) to 19 (lowest).Priority is given to a job so that the most important job is executed first by the kernel and then the other least important job
- Show all ruby-related PIDs and processes
pgrep -fl ruby
- Whats a process doing?
strace -f -p $PID
- Keep running the same command over and over
watch 'ps aux | grep ruby'
- How much memory is left
free -m
Free: memory that is currently not used for anything. It should be small since memory shouldn’t be wasted
Available: amount available for allocation to new process. Modern operating systems go out of their way to keep as little memory free as possible. Memory that is free is actually harder to use because it has to be transitioned from free to in use. Memory that is already in use, that is, memory that is available but not free, can easily be switched to another use.
The "buffers" and "cached" will be released by the kernal if they are needed.
- Are we swapping
vmstat 1
- Top 10 memory hogs
ps aux --sort=-resident|head -11
- Tail all queries running against mysql
pt-query-digest --processlist h=localhost --print --no-report --user xxxx --password *****
- Check readwrite per sec on disk
iostat -xnk 5
- How much io disk or network is getting or sending
dstat
- Show every call a program is making
strace python myprogram.py #dont run on production db
opensnoop -p pid #same as strace but won't slow u down
- Show current directory disk size
du -hs
- What is using the IO? Is MySQL sucking up the resources? Is it your PHP processes?
dstat --top-io --top-bio
- top 10 memory hogs
ps aux --sort=-resident|head -11
- Tracroute but Avoid tcp blockage
tcptraceroute google.com
- is the host oversold
top, look for %st. Stealtime = virtual machines are competing for resources.
If %st increases on all VM's, means your VM is using too much cpu.
elif %st increases on just one VM = Physical is oversold
- Disk performance
A sustained increase of VolumeQueueLength way above 1 on a standard EBS volume should be treated as exhausting the throughput of that EBS volume. We recommend that you target a queue length between 4 and 8 for volumes with 2,000 to 4,000 provisioned IOPS, or a queue length of 1 for every 500 IOPS provisioned for volumes with fewer than 2,000 provisioned IOPS
-
Bandwidth available between two computers
iperf -s -
Test if a specific TCP/IP port is open with round trip
hping3 www.google.com -S -V -p 443 -S Sets the SYN tcp flag -
View Services Startup
chkconfig --list -
Runlevels
Red Hat as well as most of its derivatives (such as CentOS) uses runlevels like this:
ID Description
0 Halt
1 Single user
2 Full multi-user with no networking
3 Full multi-user, console logins only
4 Not used/User definable
5 Full multi-user, with display manager as well as console logins
6 Reboot
The default runlevel is set in the /etc/inittab file with the :initdefault: entry
The default run level is 5. To disable a
service, run the following command:
/sbin/chkconfig servicename off
Unless they are required, disable the following:
anacron haldaemon messagebus apmd hidd microcode_ctl autofs` hplip* pcscd avahi-daemon* isdn readahead_early bluetooth kdump readahead_later cups* kudzu rhnsd* firstboot mcstrans setroubleshoot gpm mdmonitor xfs.
Items marked with a * are network services. It is particularly important to disable these. Additionally, the following services can be safely disabled if NFS is not in use: netfs, nfslock, portmap, rpcgssd, and rpcidmapd. Some software relies on haldaemon and messagebus, so care should be taken when disabling them
-
Auto Start Service
chkconfig httpd on -
Restart Service
/etc/init.d/<servicename> Service <servicename> restart -
Reload Service configuration
kill -HUP 128 This causes the program to restart and examine its configuration files.
-
Xargs: Get input from a pipe and run a command for each argument. takes strings separated by whitespace and passes them into the command specficied
ls |xargs -n 2 echo #-n2 means how many arguments to supply at a given time -
Awk
https://www.howtogeek.com/562941/how-to-use-the-awk-command-on-linux/
find positional parameters
ls -la | awk '{ print $ 5}’
- Awk (continued)
awk '{ print $2, $1 }' file # Print and inverse first two columns
awk '{printf("%5d : %s\n", NR,$0)}' file # Add line number left aligned
awk '{print FNR "\t" $0}' files # Add line number right aligned
awk NF test.txt # remove blank lines (same as grep '.')
awk 'length > 80' # print line longer than 80 char)
$0 Represents the entire line of text.
$1 Represents the first field.
$NF Stands for “number of fields,” and represents the last field.
- Awk (output field seperators)
put a / after each output
date | awk 'OFS="/" {print$2,$3,$6}'
- Awk (begin and ends)
put a line before everything runs
awk 'BEGIN {print "Dennis Ritchie"} {print $0}' dennis_ritchie.txt
- Awk (input field seperators)
If you want awk to work with text that doesn’t use whitespace to separate fields, you have to tell it which character the text uses as the field separator. For example, the /etc/passwd file uses a colon (:) to separate fields.
awk -F: '{print $1,$6}' /etc/passwd
- Awk (patterns)
If all we’re interested in are regular user accounts, we can include a pattern with our print action to filter out all other entries. Because User ID numbers are equal to, or greater than, 1,000, we can base our filter on that information.
awk -F: '$3 >= 1000 {print $1,$6}' /etc/passwd
- cut
Get the second field delimited by a dot
cut -f2 -d "."
- Sed
sed 's/string1/string2/g' # Replace string1 with string2
sed -i 's/wroong/wrong/g' *.txt # Replace a recurring word with g
sed 's/\(.*\)1/\12/g' # Modify anystring1 to anystring2
sed '/<p>/,/<\/p>/d' t.xhtml # Delete lines that start with <p>
# and end with </p>
sed '/ *#/d; /^ *$/d' # Remove comments and blank lines
sed 's/[ \t]*$//' # Remove trailing spaces (use tab as \t)
sed 's/^[ \t]*//;s/[ \t]*$//' # Remove leading and trailing spaces
sed 's/[^*]/[&]/' # Enclose first char with [] top->[t]op
sed = file | sed 'N;s/\n/\t/' > file.num # Number lines on a file
Regular Expressions
http://www.grymoire.com/Unix/Sed.html
-
Tail, Sort, Head
ps -aux | tail -n +2 | sort -rnk 4 tail = starting from 2 lines below otp sort = - reverse , numeric sort, by column 4 head = output the first 10 lines uniq = with -c counts how many times a string shows up in a document uniquely -
run jobs in parallel easily:
ls *.png | parallel -j4 convert {} {.}.jpg -
Open an editor to work with long or complex command lines
ctrl-x ctrl-e -
Wait until [command 1] is finished to execute [command 2]
[command 1] ; [command 2] -
To leave stuff in background even if you logout
nohup ./long_script & -
Change to the previous directory you were working on
cd - -
Starts a command at the specified time
echo start_backup.sh | at midnight -
Remembers your most used folders
'j.py' http://tiny.cc/62qjow an incredible substitute to browse directories by name instead of 'cd' - learn to use 'pushd' to save time navigating folders (j.py is better though)tee: allows you to pipe output to a file and stdout at the same timeawk: finds patterns in files. most useful for filtering fields seperated by white spacetr: translates characters ie: upper to lowercase, removing whitespace, extra characters.cut: used to select a number of characters or columns from an input.tac: reverse cat. shows last line at the topcurl: used for transferring data. useful for testing web connections.wget: usually used for downloading files from the webwatch: used to repeat a command periodically. Useful for watching files or proceses.head: shows the beginning of a file(s)tail: shows the end of a file(s)
-
Explain the following command:
(date ; ps -ef | awk '{print $1}' | sort | uniq | wc -l ) >> Activity.log- Shows the date
- show all processes by users including extra information such as userid
- select the first column (uid)
- sort by id
- remove duplicate userid
- count number of entries
- pip to file
-
Output redirection
> file redirects stdout to file 1> file redirects stdout to file 2> file redirects stderr to file &> file redirects stdout and stderr to file -
Write output to a file
cat <<EOF> ~/.kube/config
apiVersion: v1
clusters:
EOF
Login vs Non-Login:
Login: When you login via SSH or via console without GUI. (Mac: Terminal, iTerm), Fabric
Non-Login: from desktop if you open xterm (except on mac), screen command
Test which one: shopt login_shell
Ubuntu:
Login shell: Loads .profile > source .bashrc
Non-login(already logged): Loads .bashrc only
* if .bash_profile is present . it will be loaded first. If you want to load .profile you must source it in bash_profile
Mac:
Login: Gui, iTerm and Terminal are loaded as login .
.bash_profile is loaded > source .bashrc
.bashrc - is for bash configs
.profile/.bash_profile : environmentmal variables
- Configure defaul shell
defshell -bash
- Adding aliases
in your .bashrc
alias dev='ssh fooey@dev.example.com -p 22000'
- Make bash history 10,0000
export HISTSIZE=100000 SAVEHIST=100000 HISTFILE=~/.bash_history
- Configure command line completion using up and down arrows
Create ~/.inputrc and fill it with this:
"\e[A": history-search-backward
"\e[B": history-search-forward
set show-all-if-ambiguous on
set completion-ignore-case on
- Colorize Bash Prompt
add to .bash_profile
export PS1="[\[\e[32;1m\]\u@\h \[\e[33;1m\]\W\[\033[m\]]\[\e[37;1m\]\$ "
- to run a command from history use exclamation !
!680
- Prompt for input in a bash script
read -p “Do you want to continue” variable
- Cut off the first column in a text file
cat filename | cut -d" " -f1
- Redirection of output
&> for redirection, it redirects both the standard output and standard error
- Find what a command does
whatis
The whatis command displays a summary line from the man page for the specified command.
- Navigation
ctrl-w - delete the last word
ctrl-u - delete start of the line
ctrl-l - clear the screen
cd - : go back to previous working dir
option-left/right - move word by word
- Loop through text file
for repo in $(cat repos.txt)
do
echo $repo
done
- Loop through folders
for d in */ ; do
echo "$d"
cd $d
<<comand here>>
cd ..
done
- Base64 Decode
echo "word" | base64 -d
- set variable
FOO="bar"
- unset variable
unset FOO
- recalling your variable by prepending it with a dollar sign ($).
echo $FOO
- preserves any special characters that might appear in the variable;
echo "${FOO}"
-
Prepending
When you create a variable, the variable is known to your current shell and only your current shell You can prepend any number of variables before running a command. Whether the variables are used by the child process is up to the process, but you can pass the variables to it no matter what:
$ FOO=123 bash $ echo $FOO 123
-
Exporting variables
Another way to make variables available to a child process is the export keyword, a command built into Bash. The export command broadens the scope of whatever variable or variables you specify:
-
Bash script header
#!/bin/bash
- Bash loop
for f in * ;
do file $f ;
done
or 1 liner
for f in * ; do convert $f -scale 33% tmp/$f ; done
-
Zshell
.zprofile is equivalent to .bash_profile and runs at login, including over SSH .zshrc is equivalent to .bashrc and runs for each new Terminal session
-
Redirects
# cmd 1> file # Redirect stdout to file.
# cmd 2> file # Redirect stderr to file.
# cmd 1>> file # Redirect and append stdout to file.
# cmd &> file # Redirect both stdout and stderr to file.
# cmd >file 2>&1 # Redirects stderr to stdout and then to file.
# cmd1 | cmd2 # pipe stdout to cmd2
# cmd1 2>&1 | cmd2 # pipe stdout and stderr to cmd2
- Variables
MESSAGE="Hello World" # Assign a string
PI=3.1415 # Assign a decimal number
- Arguments
$0, $1, $2, ... # $0 is the command itself
$# # The number of arguments
$* # All arguments (also $@)
- Special Variables
$$ # The current process ID
$? # exit status of last command
command
if [ $? != 0 ]; then
echo "command failed"
fi
mypath=`pwd`
mypath=${mypath}/file.txt
echo ${mypath##*/} # Display the filename only
echo ${mypath%%.*} # Full path without extention
foo=/tmp/my.dir/filename.tar.gz
path = ${foo%/*} # Full path without extention
var2=${var:=string} # Use var if set, otherwise use string
# assign string to var and then to var2.
size=$(stat -c%s "$file") # get file size in bourne script
filesize=${size:=-1}
- Constructs
for file in `ls`
do
echo $file
done
count=0
while [ $count -lt 5 ]; do
echo $count
sleep 1
count=$(($count + 1))
done
myfunction() {
# $1 is first argument of the function
find . -type f -name "*.$1" -print
}
myfunction "txt"
- Generate a file
MYHOME=/home/colin
cat > testhome.sh << _EOF
# All of this goes into the file testhome.sh
if [ -d "$MYHOME" ] ; then
echo $MYHOME exists
else
echo $MYHOME does not exist
fi
_EOF
sh testhome.sh
- Assigning output of one command to variable
#!/bin/bash
for node in $(cat nodes.txt)
do
node_name=$(echo $node | tr -d '"');
echo $node_name
done
- Iterating a json file
for r in $(cat repos.json | jq '.[]')
do
repo_name=$(echo $r | tr -d '"');
echo $repo_name;
done
- Checking for existence of arguments
if [ $# -eq 0 ]; then
echo "Please enter an argument"
exit 1
fi
- Check for environment variable
if [ -z "${GITHUB_TOKEN}" ]; then
echo "Missing GITHUB_TOKEN environment variable"
exit 1
fi
- Checking the output of last command and prompt to continue
if [[ $? -ne 0 ]]; then
echo "command failed"
read ABCD
fi
- Iterate over a list
namespaces=(ns1 ns2 ns3)
for n in ${namespaces[@]}; do
echo "*** $n ***" ;
done
- !^
!^ maps to the first argument of your latest command.
- !$
!$ maps to the last argument of your latest command.
- !!:2
you could use the !! event designator to select the last command, and the 2 word designator to select the second argument.
- Brace expansion
expanded into ~/test/pics , ~/test/sounds, ~/test/sprites
$ mkdir ~/test/{pics,sounds,sprites}
A brace expansion can also have a sequence pattern {x..y[..incr]} where x and y are either an integer or a single character, and incr is an optional increment value.
touch ~/test/sounds/noise-{1..5}.mp3
$ touch ~/test/pics/pic{1..10..2}.jpg
$ ls ~/test/pics
pic1.jpg pic3.jpg pic5.jpg pic7.jpg pic9.jpg
- Command Expansion
Your shell can replace a command surrounded by $() with its output.
$ cat <<EOF > aboutme
My name is $(whoami)
and I live in $HOME
EOF
$ cat aboutme
My name is br
and I live in /home/br
for example rename all directories to uppercase
$ for dir in */; do
mv "$dir" "$(echo "$dir" | tr '[:lower:]' '[:upper:]')"
done
- Copy from clipboard into new file
cat > generate-conf.sh (ctrl+d = paste)
- set -e
The set -e option instructs bash to immediately exit if any command [1] has a non-zero exit status. You wouldn't want to set this for your command-line shell, but in a script it's massively helpful. In all widely used general-purpose programming languages, an unhandled runtime error
-
whether that's a thrown exception in Java, or a segmentation fault in C, or a syntax error in Python - immediately halts execution of the program; subsequent lines are not executed.
- By default, bash does not do this. This default behavior is exactly what you want if you are using bash on the command line
- you don't want a typo to log you out! But in a script, you really want the opposite.
- If one line in a script fails, but the last line succeeds, the whole script has a successful exit code. That makes it very easy to miss the error.
- Again, what you want when using bash as your command-line shell and using it in scripts are at odds here. Being intolerant of errors is a lot better in scripts, and that's what set -e gives you.
- set -x
Enables a mode of the shell where all executed commands are printed to the terminal. In your case it's clearly used for debugging, which is a typical use case for set -x : printing every command as it is executed may help you to visualize the control flow of the script if it is not functioning as expected.
- set -u
Affects variables. When set, a reference to any variable you haven't previously defined - with the exceptions of
```
#!/bin/bash
firstName="Aaron"
fullName="$firstname Maxwell"
echo "$fullName"
```
Take a moment and look. Do you see the error? The right-hand side of the third line says "firstname", all lowercase, instead of the camel-cased "firstName". Without the -u option, this will be a silent error. But with the -u option, the script exits on that line with an exit code of 1, printing the message "firstname: unbound variable" to stderr.
This is what you want: have it fail explicitly and immediately, rather than create subtle bugs that may be discovered too late.
- set -o pipefail
30 years ago, when the first users of Bourne shell were burned by this problem, a shell option called “pipefail” was introduced. Enabling this option changes the shell’s behavior so that, when any command in a pipeline series fails, the entire pipeline fails. However, this option is not enabled by default, so it’s widely recommended as best practice that all scripts should start by enabling this (and a few other) (options)[https://sipb.mit.edu/doc/safe-shell/].
This setting prevents errors in a pipeline from being masked. If any command in a pipeline fails, that return code will be used as the return code of the whole pipeline. By default, the pipeline's return code is that of the last command even if it succeeds. Imagine finding a sorted list of matching lines in a file:
```
$ grep some-string /non/existent/file | sort
grep: /non/existent/file: No such file or directory
% echo $?
0
```
-
Here, grep has an exit code of 2, writes an error message to stderr, and an empty string to stdout.
-
This empty string is then passed through sort, which happily accepts it as valid input, and returns a status code of 0.
-
This is fine for a command line, but bad for a shell script: you almost certainly want the script to exit right then with a nonzero exit code... like this:
$ set -o pipefail $ grep some-string /non/existent/file | sort grep: /non/existent/file: No such file or directory $ echo $? 2
- Setting IFS
The IFS variable - which stands for Internal Field Separator - controls what Bash calls word splitting. When set to a string, each character in the string is considered by Bash to separate words. This governs how bash will iterate through a sequence. For example, this script:
```
#!/bin/bash
IFS=$' '
items="a b c"
for x in $items; do
echo "$x"
done
IFS=$'\n'
for y in $items; do
echo "$y"
done
... will print out this:
a
b
c
a b c
```
In the first for loop, IFS is set to
For the first loop, IFS is a space, meaning that words are separated by a space character. For the second loop, "words" are separated by a newline, which means bash considers the whole value of "items" as a single word. If IFS is more than one character, splitting will be done on any of those characters.
Got all that? The next question is, why are we setting IFS to a string consisting of a tab character and a newline? Because it gives us better behavior when iterating over a loop. By "better", I mean "much less likely to cause surprising and confusing bugs". This is apparent in working with bash arrays:
```
#!/bin/bash
names=(
"Aaron Maxwell"
"Wayne Gretzky"
"David Beckham"
)
echo "With default IFS value..."
for name in ${names[@]}; do
echo "$name"
done
echo ""
echo "With strict-mode IFS value..."
IFS=$'\n\t'
for name in ${names[@]}; do
echo "$name"
done
```
```
## Output
With default IFS value...
Aaron
Maxwell
Wayne
Gretzky
David
Beckham
With strict-mode IFS value...
Aaron Maxwell
Wayne Gretzky
David Beckham
```
Or consider a script that takes filenames as command line arguments:
```
for arg in $@; do
echo "doing something with file: $arg"
done
```
If you invoke this as myscript.sh notes todo-list 'My Resume.doc', then with the default IFS value, the third argument will be mis-parsed as two separate files - named "My" and "Resume.doc". When actually it's a file that has a space in it, named "My Resume.doc".
Which behavior is more generally useful? The second, of course - where we have the ability to not split on spaces. If we have an array of strings that in general contain spaces, we normally want to iterate through them item by item, and not split an individual item into several.
Setting IFS to $'\n\t' means that word splitting will happen only on newlines and tab characters. This very often produces useful splitting behavior.
By default, bash sets this to $' \n\t' - space, newline, tab - which is too eager.
- Show Hostname
hostname -f
- Set hostname
hostname acme.dev.nul
or /etc/sysconfig/network
- Change Time Zone
ln -sf /usr/share/zoneinfo/Australia/Sydney /etc/localtime
export TZ=Australia/Sydney
- Show IP
hostname -I
ip addr show
sudo ethtool eth0 - show connection status
- Set IP
ifconfig eth0 192.168.0.10 netmask 255.255.255.0
system-config-network
/etc/sysconfig/network-scripts/
ip address add 192.168.0.1 dev eth0
- Add Default Gateway
route add default gw xx.xx.xx.1
- Restart Nic
service network restart
/etc/init.d/network restart
ifup eth0
- Configure DNS
nano /etc/resolv.conf
- Configure DNS for specific suffix
cat /etc/resolver/private
nameserver 192.168.99.100
- Query DNS
dig +short txt 20120113._domainkey.gmail.com @8.8.8.8 #query text records
dig -x host #reverse
dig +nocmd +noall +answer www.blah.com #shows TTL
dig +short txt u123455.wl0000.sendgrid.net #query spf txt records
dig +short mx company.com # query mx records
- Wget
* Download file setting target directory:
wget -P ~/dest/dir www.foo.com/myfile.png
* Download file but save as different name
wget -O taglist.zip http://www.vim.org/scripts/download_script.php
- Curl
curl -I www.server.com # -I to show headers only, -i to show headers
curl -D- www.server.com |less # shows detailed tcp stuff
- Curl loop
while true; do curl --write-out " - HTTP Response: %{http_code} - Total time: %{time_total} \n" https://google.com; done #continous
- Show IP address
curl ipinfo.io
- Siege
* Benchmark 20 connections for 30 seconds.
siege -c20 www.google.com -b -t30s
- Ngrep
* Similar to wireshark
ngrep -q -W byline "^(GET|POST) .*" # -W byline preserves linesbreaks, -q #supresses output about non-matching packets
ngrep -q -W byline "search" host www.google.com and port 80
* Show packets going to a website on network
ngrep -d mywebsite
- Portscan
nc -z example.com 20-100 #scan port 20-100
- Copy files between two hosts
Server: $ nc -l 9090 | tar -xzf -
Client: tar -czf dir/ | nc server 9090
- Expose a shell over port 8080
server:
$ mkfifo backpipe $ nc -l 8080 0<backpipe | /bin/bash > backpipe
Client:
nc example.com 8080
- receive file
nc -l 9931 > bigfile
- send file
cat bigfile | nc ipaddress 9931
nc -l -p 1234 #starts a server on port 1234
nc destination_host 1234 # connect to server from client
tar cfp - /some/dir | compress -c | nc -w 3 destination_host 1234 # compress file and send to remove
- Tunnel traffic to any server you have ssh access to including dns
sshuttle -r <server> --dns 0/0
Allows you to inspect https traffic
- Automatically strip all cache control headers and make sure you always get fresh connection
mitmproxy --anticache
- Record a session
mitmdump -w user-signup
- Replay a sessio
mitmdump -c user-signup | tail -n1 | grep 200 && echo "OK" || echo "FAIL"
- Disable ping to avoid ICMP flood
Set following in /etc/sysctl.conf : net.ipv4.icmp_echo_ignore_all = 1
Then “sysctl -p”
- Show Public IP Address
ip addr show eth0 | grep inet | awk '{ print $2; }' | sed 's/\/.*$//'
- Show SYN Flood
ss -a | grep SYN-RECV | awk '{print $4}' | awk -F":" '{print $1}' | sort | uniq -c | sort -n
or
netstat -antp | grep SYN_RECV|awk '{print $4}'|sort|uniq -c | sort -n
- Config File
~/.screenrc
- Commands
screen -ls #show all screens
CTRL a w # which screens are available
CTRL a 0 # go to window 0
CTRL a 1 # go to window 1
CTRl a D # detach from current session
CTRL a c # create a new screen
CTRL a n # go to next screen
CTRL a A # rename session name
CTRL a S # split screen horizontal
CTRL a TAB # move to next split screen
CTRL a | # split screen vertical
CTRL A X # close current split screen
CTRL+a - switches to last window
Exit # kill current session
screen -r #reattach to screen
- update pip (Python package manager):
pip install -U pip
- search pip repos
pip
- create a virtual python environment
virtualenv [dirname] --no-site-packages
- connect to a virtual python environment
source [dirname]/bin/activate
- disconnect from a python environment:
deactivate
- install package into virtual python environment from outsie:
pip install [packagename]==[version_number] -E [dirname]
- export python virtual environment into a shareable format:
pip freeze -E [dirname] > requirements.txt
- import python virtual environment from a requirements.txt file:
pip install -E [dirname] -r requirements.txt
- Share all files in current folder over port 8080
python -m SimpleHTTPServer 8080
- Show config
iptables -L -v
- Edit config
/etc/sysconfig/iptables
- Allow connections for all tcp connections attempts at web connections.
sudo iptables -I INPUT 2 -p tcp --dport 80 -j ACCEPT
- Lockdown connections to any IP address lying in the range of 192.168.1.0 - 192.168.1.255
sudo iptables -I INPUT 2 -p tcp --dport 22 -s 192.168.1.0/24 -j ACCEPT
- Lockdown SSH to kick anyone after 3 attempts
Replace default ssh rule with this one.
The first rule records the IP address of each attempt to access port 22 using the recent module.
The second rule checks to see if that IP address has attempted to connect 4 or more times within the last 60 seconds, and if not then the packet is accepted.
Note this rule would require a default policy of DROP on the input chain.
iptables -A INPUT -p tcp --dport 22 -m recent --set --name ssh --rsource
iptables -A INPUT -p tcp --dport 22 -m recent ! --rcheck --seconds 60 --hitcount 4 --name ssh --rsource -j ACCEPT
- Command switches
-A Append
-I Inserts rule to position in chain
-m Connection State
-j jump to target: Accept, Drop, Log
--dport destination port
-s source ip
-p protocol
- Save config
/etc/init.d/iptables save
- Restart Iptables
sudo /sbin/service iptables restart
- Disable SE Linux
cat /etc/selinux/config
SELINUX=disabled
SELINUXTYPE=targeted
- Check repositories:
nano /etc/yum.repos.d/CentOS-Base.repo sudo yum repolist
* Install Repositories
rpm -Uvh http://packages.sw.be/rpmforge-release/rpmforge-release-0.5.2-2.el6.rf.x86_64.rpm
* Install package
yum install PACKAGENAME
* Remove package
yum remove PACKAGENAME
* Update package
yum update PACKAGENAME
* List available updates
yum list updates
* Update system
yum update
* Upgrade system to newest release (dangerous!)
yum upgrade
* Show package
yum list PACKAGENAME
* Search package repositories
yum search SEARCHSTRING
* Search particular version of a package
yum --showduplicates list httpd | expand
* List package groups
yum grouplist
* Install package group
yum groupinstall 'GROUP NAME'
* Update package group
yum groupupdate 'GROUP NAME'
* Remove package group
yum groupremove 'GROUP NAME'
* Install utitilites you would need to install most commonly
yum groupinstall "Development Tools"
* Show installed packages
yum list installed
* Show available updates
yum list updates
## Cron
* Cron files
/etc/cron.allow # users allowed to submit jobs
* Jobs submitted from following dirs
/etc/crontab # root only jobs /etc/cron.d # /etc/cron.hourly #files placed in this dir run hourly /var/spool/cron/username # created for user when run crontab -e
* Crontab Commands
export EDITOR=nano to specify a editor to open crontab file. crontab -e Edit your crontab file, or create one if it doesn’t already exist. crontab -l Display your crontab file. crontab -r Remove your crontab file. crontab -v Display the last time you edited your crontab file. (This option is only available on a few systems.)
* Crontab file
Crontab syntax : A crontab file has five fields for specifying day , date and time followed by the command to be run at that interval.
-
* * * * command to be executed
| | | | | | | | | +----- day of week (0 - 6) (Sunday=0) | | | +------- month (1 - 12) | | +--------- day of month (1 - 31) | +----------- hour (0 - 23) +------------- min (0 - 59)
* To Use Env Variables
Example:
- In crontab -e file:
SHELL=/bin/bash */1 * * * * $HOME/cron_job.sh
- In cron_job.sh file: #!/bin/bash source $HOME/.bash_profile some_other_cmd
* To Run with Virtual Env
-
in cron.sh #!/bin/bash source $HOME/.bash_profile source /home/user/envs/project/bin/activate python ~/projects/myproject/myproject/cron.py >> ~/cronstatus.log
-
in cron.py
import os os.environ.setdefault("DJANGO_SETTINGS_MODULE", "myproject.settings") from django.conf import settings
* Generate log file
30 18 * * * rm /home/someuser/tmp/* > /home/someuser/cronlogs/clean_tmp_dir.log
* Find out what cron jobs are running
ls /etc/cron* + cat for user in $(cat /etc/passwd | cut -f1 -d:); do crontab -l -u $user; done
* To find out where is cron log
grep -ic cron /var/log/* | grep -v :0
grep cron /etc/rsyslog.conf
* Check if cron configured to log
cat /etc/default/cron
look for EXTRA_OPTS="-L 2” -L is how verbose
* Check cron log
mailx
#SSH
* SSHD Config
nano /etc/ssh/sshd_config
* User Config File
~/.ssh/config
* Example Config
Host dev
HostName dev.example.com
Port 22000
User phooey
IdentityFile ~/.ssh/github.key
* Port Forwarding
* Local client will use 9906 and use ssh and connect over to 3306
ssh -f -N -L 9906:127.0.0.1:3306 user@remoteserver.com
* Lightweight Proxy for Geoblocked content:
ssh -D 9090 user@remoteserver.com
Exposes the local port 9090 as a SOCKS proxy. You can then alter your browser settings to use your local SOCKS proxy to route browsing traffic.
* Port Forwarding Shortcut
Add this to your ssh config to make it easier to call tunnel
Host tunnel
Host name remoteserver.com
Local forward 9906 127.0.0.1:3306
ssh -f -N tunnel
* Create a new user on the server
Generate a SSH key on local machine
ssh-keygen -t rsa -C "your_email@example.com"
Upload the key to the server and add it website user’s authorised keys
scp i secure_keypair.pem ~/.ssh/id_rsa.pub ec2-user@newwebsite.com:/tmp/ cd ~/ mkdir .ssh cat /tmp/id_rsa.pub > .ssh/authorized_keys chmod 700 .ssh chmod 600 .ssh/authorized_keys sudo rm /tmp/id_rsa.pub
Or Upload key to server ussing ssh-copy-id
ssh-copy-id [-i [identity_file]] [user@]machine
* Configure SSH Login using Keys
nano /home/deploy/.ssh/authorized_keys
Add the contents of the id_rsa.pub on your local machine and any other public keys that you want to have access to this server to this file
chmod 600 .ssh/authorized_keys
* Configure SSH For Certain Users or logins
nano /etc/ssh/sshd_config
Add these lines to the file, inserting the ip address from where you will be connecting:
PermitRootLogin no
PasswordAuthentication no
AllowUsers user@(your-ip) user@(another-ip-if-any)
* Run Commands on remote machine
ssh -l <username> <servername> "/bin/cat -n /etc/group"
* Access Localhost pages on remote system
Note that if you are working with a remote system via SSH, you can't directly access the remote box's localhost URL. A solution to this is to simply forward port from the remote machine to your local machine:
ssh -f -N -L 8081:localhost:8081 your_user@your_remote_machine
Now you can access http://localhost:8081 and it will be as if you would issue the request from the remote machine.
* Prevent Idle SSH sessions being killed
Client config
ServerAliveInterval = 60
Server config
ClientAliveInternal = 60
* Retreive the public key from a private key
ssh-keygen -y -e -f myfile.pem
* Enable Bastion Host
On local machine enable SSH Agent forwarding
ssh -A user@bastion
or
Host bastion
ForwardAgent yes
Then configure ProxyCommand setting for the remote instances in your SSH configuration file.
Host private1
IdentityFile ~/.ssh/rsa_private_key
ProxyCommand ssh user@bastion -W %h:%p
Host bastion
IdentityFile ~/.ssh/bastion_rsa_key
ForwardAgent yes
Finally, connect to private instance
ssh user@private1
SSH will establish a connection to the bastion host and then from the bastion host connect to “private1”, using the specified keys at each step along the way.
* SSH Multiplexing
SSH multiplexing is the ability to carry multiple SSH sessions over a single TCP connection. This can result in speed increases that can add up when repeatedly running commands against remote SSH hosts.
Host demo-server.domain.com
ControlPath ~/.ssh/cm-%r@%h:%p
ControlMaster auto
ControlPersist 10m
The ControlPath entry specifies where to store the “control socket” for the multiplexed connections. In this case, %r refers to the remote login name, %h refers to the target host name, and %p refers to the destination port.
The ControlMaster setting is what activates multiplexing. With the auto setting, SSH will try to use a master connection if one exists, but if one doesn’t exist it will create a new one (this is probably the most flexible approach, but you can refer to ssh-config(5) for more details on the other settings).
Finally, the ControlPersist setting keeps the master connection alive for the specified period of time after it has remained idle (no connections).
* Ansible Through Bastion
Custom SSH configuration file is useless without explicitly telling Ansible to use these settings when connecting to Ansible-managed hosts. This is accomplished by creating (or modifying) ansible.cfg and adding the following setings:
[ssh_connection]
ssh_args = -F ./ssh.cfg -o ControlMaster=auto -o ControlPersist=30m
control_path = ~/.ssh/ansible-%%r@%%h:%%p
* Do programs remain running when you disconnect?
The new default is to kill all children of a terminating login session, regardless of what historically valid precautions were taken to prevent this. The behavior can be changed by setting KillUserProcesses=no in /etc/systemd/logind.conf. When the SSH daemon process associated with your connection decides that your connection is dead, it sends a hangup signal (SIGHUP) to the login shell. This notifies the shell that you've vanished and that it should begin cleaning up after itself. What happens at this point is shell specific (search its documentation page for "HUP"), but for the most part it will start sending SIGHUP to running jobs associated with it before terminating. Each of those processes, in turn, will do whatever they're configured to do on receipt of that signal. Processes that were invoked with a prefixed nohup command. (i.e. "don't hang up on this") Daemons interpret the HUP signal differently; since they do not have a controlling terminal and do not automatically receive a HUP signal
* Access RDS in a Private Subnet from Local Machine
ssh -i "Private_key.pem" -f -N -L 3306:RDS_Instance_Endpoint:3306 ec2-user@EC2-Instance_Endpoint -v
ssh -i ~/.ssh/my.key -f -N -L
3306:rdshostname.cluster-xyz.us-west-2.rds.amazonaws.com:3306
ec2-user@ec1-2-3-4.us-west-2.compute.amazonaws.com -v
## Apache
* Install
sudo yum install httpd mod_ssl
sudo yum install httpd24 mod_ssl
* Make DocumentRoot
mkdir /var/www/website.com
* Edit config
sudo nano /etc/httpd/conf/httpd.conf
* ServerAdmin
ServerAdmin admin@website.com
* ServerName
www.website.com
* DocumentRoot
DocumentRoot "/var/www/website.com"
* Directory Options
<Directory "/var/www/website.com">
Options FollowSymLinks #Comment out Indexes to prevent browsing of directories
* ServerTokens
ServerTokens Prod # only shows Apache
* Default: full
* Timeout
Timeout 30 # is the max time to wait for a response, action it and respond. Forces visitors to wait in line.
* Default : 60
* MaxKeepAliveRequests
MaxKeepAliveRequests 200 #max number of requests per connection
*Default : 100
* KeepAliveTimeout
KeepAliveTimeout 3 #time that the connection waits for client to request something. But new connections will be on hold. Lower is best
* Default : 5
* LoadModule
Remove Following LoadModule auth_basic_module modules/mod_auth_basic.so -basic auth- LoadModule auth_digest_module modules/mod_auth_digest.so - md5 authentication LoadModule authn_file_module modules/mod_authn_file.so - auth using text files LoadModule authn_alias_module modules/mod_authn_alias.so - mapping to different parts of file system LoadModule authn_anon_module modules/mod_authn_anon.so - allows anonymous access to authenticated areas LoadModule authn_dbm_module modules/mod_authn_dbm.so - auth using dbm files LoadModule authn_default_module modules/mod_authn_default.so - #doesnt exist in 2.4? LoadModule authz_host_module modules/mod_authz_host.so - auth based on hostname LoadModule authz_user_module modules/mod_authz_user.so - user auth? LoadModule authz_owner_module modules/mod_authz_owner.so - auth based on file owner LoadModule authz_groupfile_module modules/mod_authz_groupfile.so - auth based on plaintext file LoadModule authz_dbm_module modules/mod_authz_dbm.so LoadModule authz_default_module modules/mod_authz_default.so #LoadModule ldap_module modules/mod_ldap.so - ldap connection pooling and caching #LoadModule authnz_ldap_module modules/mod_authnz_ldap.so - ldap auth LoadModule include_module modules/mod_include.so - server parsed html docs LoadModule log_config_module modules/mod_log_config.so - log requests to the server LoadModule logio_module modules/mod_logio.so - logging of input output bytes #LoadModule env_module modules/mod_env.so - modifies environment for cgi files #LoadModule ext_filter_module modules/mod_ext_filter.so - pass responses to a filter before client (potentially need) LoadModule mime_magic_module modules/mod_mime_magic.so LoadModule expires_module modules/mod_expires.so - creation of expires http headers LoadModule deflate_module modules/mod_deflate.so -compress content LoadModule headers_module modules/mod_headers.so - customized headers #LoadModule usertrack_module modules/mod_usertrack.so - clickstream logging LoadModule setenvif_module modules/mod_setenvif.so - set env variables based on request LoadModule mime_module modules/mod_mime.so - associates extension with content type #LoadModule dav_module modules/mod_dav.so - webdav #LoadModule status_module modules/mod_status.so - info on server perf and activity LoadModule autoindex_module modules/mod_autoindex.so -creates indexes #LoadModule info_module modules/mod_info.so - overview of server config #LoadModule dav_fs_module modules/mod_dav_fs.so -webdav LoadModule vhost_alias_module modules/mod_vhost_alias.so LoadModule negotiation_module modules/mod_negotiation.so LoadModule dir_module modules/mod_dir.so #LoadModule actions_module modules/mod_actions.so - executes cgi scripts based on media type LoadModule speling_module modules/mod_speling.so - corrects incorrect urls #LoadModule userdir_module modules/mod_userdir.so - allows access to ~/john LoadModule alias_module modules/mod_alias.so LoadModule substitute_module modules/mod_substitute.so LoadModule rewrite_module modules/mod_rewrite.so #LoadModule proxy_module modules/mod_proxy.so #LoadModule proxy_balancer_module modules/mod_proxy_balancer.so #LoadModule proxy_ftp_module modules/mod_proxy_ftp.so #LoadModule proxy_http_module modules/mod_proxy_http.so #LoadModule proxy_ajp_module modules/mod_proxy_ajp.so #LoadModule proxy_connect_module modules/mod_proxy_connect.so LoadModule cache_module modules/mod_cache.so #LoadModule suexec_module modules/mod_suexec.so - allow cgi scripts to run as specific user LoadModule disk_cache_module modules/mod_disk_cache.so #LoadModule cgi_module modules/mod_cgi.so - excute cgi #LoadModule version_module modules/mod_version.so - used if you want directives for different httpd versions #LoadModule mod_lua - provides interfaces for lua programming language
* Server Signature
ServerSignature Off
* Default: On
* Virtual Host
#Virtual Host <VirtualHost *:80> ServerAdmin admin@website.com DocumentRoot /var/www/website.com ServerName www.website.com ErrorLog /var/log/httpd/website-error_log.log CustomLog /var/log/httpd/website-access_log.log common #only allow betauser while in beta AuthType Basic AuthName "Invitation Only" AuthUserFile /var/www/passwd/passwords Require user betauser
<Directory "/var/www/website.com">
# Enable rewrite engine and route requests to framework
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-l
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteCond $1 !^(api|auth)
RewriteRule ^(.*)$ index.php/$1 [L,QSA]
RewriteRule ^api/.* api/index.php [L,QSA]
RewriteRule ^auth/.* auth/index.php [L,QSA]
# Disable ETags
<IfModule mod_headers.c>
Header Unset ETag
FileETag none
</IfModule>
# Default expires header if none specified (stay in browser cache for 7 days)
<IfModule mod_expires.c>
ExpiresActive On
ExpiresDefault A604800
</IfModule>
</Directory>
- Cloudflare
Restrict /admin website to only canada and australia
SetEnvIf CF-IPCountry AU AllowCountry=1
SetEnvIf CF-IPCountry CA AllowCountry=1
<Directory /var/www/website.com/admin>
<RequireAll>
Require env AllowCountry
</RequireAll>
</Directory>
- Pagespeed
<IfModule pagespeed_module>
# Uncomment the following line if you want to disable statistics entirely.
# ModPagespeedStatistics off
# This page shows statistics about the mod_pagespeed module.
<Location /mod_pagespeed_statistics>
Order allow,deny
# One may insert other "Allow from" lines to add hosts that are
# allowed to look at generated statistics. Another possibility is
# to comment out the "Order" and "Allow" options from the config
# file, to allow any client that can reach the server to examine
# statistics. This might be appropriate in an experimental setup or
# if the Apache server is protected by a reverse proxy that will
# filter URLs to avoid exposing these statistics, which may
# reveal site metrics that should not be shared otherwise.
Allow from localhost
Allow from 127.0.0.1
SetHandler mod_pagespeed_statistics
</Location>
# This handles the client-side instrumentation callbacks which are injected
# by the add_instrumentation filter.
<Location /mod_pagespeed_beacon>
SetHandler mod_pagespeed_beacon
</Location>
</IfModule>
-
Enable Compression
#AdditionalCompression AddOutputFilterByType DEFLATE text/html text/plain text/xml text/css text/javascript application/x-javascript -
Add permissions writable directories
chown apache:apache -R /var/www/website.com/images/dir1 chown apache:apache -R /var/www/website.com/images/dir2 -
Restart
/etc/init.d/httpd restart -
Autostart
sudo /sbin/chkconfig --levels 235 httpd on -
Reload Config
sudo /etc/init.d/httpd reload -
See loaded modules
/usr/sbin/httpd -M -
Security Testing
wget -P ~/tools http://www.cirt.net/nikto/nikto-current.tar.gz tar -xzvf nikto-current.tar.gz perl nikto.pl -h localhost
-
Install tools
yum install openssl openssl-devel or yum install crypto-utils -
Generate Private Key
openssl genrsa -out my-private-key.pem 2048 or genkey --days 365 servername.domain.com -
Create CSR
openssl req -sha256 -new -key ~/my-private-key.pem -out ~/domain.com.csr -
Create a SAN config
[ req ] prompt = no default_bits = 2048 distinguished_name = req_distinguished_name req_extensions = req_ext [ req_distinguished_name ] countryName = CA stateOrProvinceName = Ontario localityName = Toronto organizationName = Company organizationalUnitName = MyBusinessUnit commonName = server.domain.com [ req_ext ] subjectAltName = @alt_names [alt_names] DNS.1 = server1.domain.com DNS.2 = server2.domain.com -
Create CSR with SAN config
openssl req -new -sha256 -key my-private-key.pem -out domain.com.csr -config san.cnf -
Verify SAN on cert
openssl req -noout -text -in domain.com.csr | grep DNS -
Convert Cert to PKCS12
openssl pkcs12 -export -out domain.com.p12 -inkey my-private-key.pem -in cert.cer -
Install Cert
Copy to /etc/httpd/conf/ssl.crt/ genkey will output /etc/pki/tls/private/ #privatekey /etc/pki/certs/ #public key -
View Cert
openssl x509 -in cerfile.cer -noout –text -
Create a self-signed certificate
openssl x509 -req -days 365 -in my.csr -signkey my-private-key.pem -out my-self-signed.pem -
Installing Root CA
Installing a CA
Copy your certificate in PEM format (the format that has ----BEGIN CERTIFICATE---- in it) into /usr/local/share/ca-certificates and name it with a .crt file extension.
Then run
sudo update-ca-certificates.
Caveats: This installation only affects products that use this certificate store. Some products may use other certificate stores; if you use those products, you'll need to add this CA certificate to those other certificate stores, too. (Firefox Instructions, Chrome Instructions, Java Instructions)
- Testing The Root CA is installed
You can verify if this worked by looking for the certificate that you just added in /etc/ssl/certs/ca-certificates.crt (which is just a long list of all of your trusted CA's concatenated together).
You can also use OpenSSL's s_client by trying to connect to a server that you know is using a certificate signed by the CA that you just installed.
$ openssl s_client -connect foo.whatever.com:443 -CApath /etc/ssl/certs
CONNECTED(00000003)
depth=1 C = US, ST = Virginia, O = "Whatever, Inc.", CN = whatever.com, emailAddress = admin@whatever.com
verify return:1
depth=0 C = US, ST = Virginia, L = Arlington, O = "Whatever, Inc.", CN = foo.whatever.com
verify return:1
---
Certificate chain
0 s:/C=US/ST=Virginia/L=Arlington/O=Whatever, Inc./CN=foo.whatever.com
i:/C=US/ST=Virginia/O=Whatever, Inc./CN=whatever.com/emailAddress=admin@whatever.com
... snip lots of output ...
Key-Arg : None
PSK identity: None
PSK identity hint: None
SRP username: None
Start Time: 1392837700
Timeout : 300 (sec)
Verify return code: 0 (ok)
The first thing to look for is the certificate chain near the top of the output. This should show the CA as the issuer (next to i:). This tells you that the server is presenting a certificate signed by the CA you're installing. Second, look for the verify return code at the end to be set to 0 (ok).
-
Test SSL certificates
openssl s_client -connect name.server.io:443 -
Certificate Formats
.csr - This is a Certificate Signing Request. Some applications can generate these for submission to certificate-authorities. The actual format is PKCS10 which is defined in RFC 2986. It includes some/all of the key details of the requested certificate such as subject, organization, state, whatnot, as well as the public key of the certificate to get signed. These get signed by the CA and a certificate is returned. The returned certificate is the public certificate (which includes the public key but not the private key), which itself can be in a couple of formats.
.pem - Defined in RFCs 1421 through 1424, this is a container format that may include just the public certificate (such as with Apache installs, and CA certificate files /etc/ssl/certs), or may include an entire certificate chain including public key, private key, and root certificates. Confusingly, it may also encode a CSR (e.g. as used here) as the PKCS10 format can be translated into PEM. The name is from Privacy Enhanced Mail (PEM), a failed method for secure email but the container format it used lives on, and is a base64 translation of the x509 ASN.1 keys.
.key - This is a PEM formatted file containing just the private-key of a specific certificate and is merely a conventional name and not a standardized one. In Apache installs, this frequently resides in /etc/ssl/private. The rights on these files are very important, and some programs will refuse to load these certificates if they are set wrong.
.pkcs12 .pfx .p12 - Originally defined by RSA in the Public-Key Cryptography Standards (abbreviated PKCS), the "12" variant was originally enhanced by Microsoft, and later submitted as RFC 7292. This is a passworded container format that contains both public and private certificate pairs. Unlike .pem files, this container is fully encrypted. Openssl can turn this into a .pem file with both public and private keys: openssl pkcs12 -in file-to-convert.p12 -out converted-file.pem -nodes A few other formats that show up from time to time:
.der - A way to encode ASN.1 syntax in binary, a .pem file is just a Base64 encoded .der file. OpenSSL can convert these to .pem (openssl x509 -inform der -in to-convert.der -out converted.pem). Windows sees these as Certificate files. By default, Windows will export certificates as .DER formatted files with a different extension. Like... .cert .cer .crt - A .pem (or rarely .der) formatted file with a different extension, one that is recognized by Windows Explorer as a certificate, which .pem is not.
.pub - public key created by openssl.
.p7b .keystore - Defined in RFC 2315 as PKCS number 7, this is a format used by Windows for certificate interchange. Java understands these natively, and often uses .keystore as an extension instead. Unlike .pem style certificates, this format has a defined way to include certification-path certificates.
.crl - A certificate revocation list. Certificate Authorities produce these as a way to de-authorize certificates before expiration. You can sometimes download them from CA websites.
In summary, there are four different ways to present certificates and their components:
PEM - Governed by RFCs, its used preferentially by open-source software. It can have a variety of extensions (.pem, .key, .cer, .cert, more)
PKCS7 - An open standard used by Java and supported by Windows. Does not contain private key material.
PKCS12 - A Microsoft private standard that was later defined in an RFC that provides enhanced security versus the plain-text PEM format. This can contain private key material. Its used preferentially by Windows systems, and can be freely converted to PEM format through use of openssl.
DER - The parent format of PEM. It's useful to think of it as a binary version of the base64-encoded PEM file. Not routinely used very much outside of Windows.
-
Install
yum install php php-cli php-common php-pecl-memcache php-pear php-mysql php-xml php-mbstring php-gd php-pdo or (amazon) yum install php54 php54-cli php54-common php54-pecl-memcache php54-pear php54-mysql php54-xml php54-mbstring php54-gd php54-pdo -
Configuration File
nano /etc/php.ini -
Expose PHP
expose_php = Off * Default: On -
Memory Limit
memory_limit = 128M * Default: 128M (no change) -
Error Log
error_log = /var/log/php-error.log * Defautl: Empty -
Timezone
date.timezone = "Australia/Sydney" -
Allow Fopen
allow_url_fopen = Off * Default : On. If enabled, allow_url_fopen allows PHP's file functions to retrieve data from remote locations such as an FTP server or web site, and could lead to code injection vulnerabilities. -
Create the PHP error files
sudo touch /var/log/php-error.log
- Database types:
The two most popular storage engines in MySQL are InnoDB and MyISAM
InnoDB supports some newer features like transactions, row-level locking, foreign keys. It's optimized for read/write high volume operations and high performance.
MyISAM is simpler and better optimized for read only operations. It has limited feature set as compared to InnoDB.
-
Get help:
help -
Login to server
mysql -h mysql–instance1.123456789012.us-east-1.rds.amazonaws.com -P 3306 -u mymasteruser -p -
Create a new Database
mysqladmin -u root -pmyPassword -v create myDB -
Show databases:
show databases; -
Secure Installation
/usr/bin/mysql_secure_installation -
Choose a database to use:
use [database name here]; -
Show database schema:
show tables; -
Delete database:
DROP DATABASE [databasename]; -
New database:
CREATE DATABASE [databasename]; -
Create a new user:
CREATE USER [username@localhost] IDENTIFIED BY '[password]' ; -
Show users:
select * from mysql.user; -
Delete a user:
delete from mysql.user WHERE User='[user_name]'; -
Give user access to all tables (make them root). the "%" means that they can sign in remotely, from any machine, not just localhost.:
grant all privileges on *.* to someusr@"%" identified by '[password]'; -
Give user access to certain database. Only accessable from localhost
grant all privileges ON myDB.* TO myUser@localhost IDENTIFIED BY 'myPassword'; -
give certain privileges to a user on a certain database:
grant select,insert,update,delete,create,drop on [somedb].* to [someusr]@["%"] identified by '[password]'; -
Show all privileges
select user,host from mysql.user ; -
Tell mysql to use new user priv policies:
flush privileges; -
change user password:
use mysql; SET PASSWORD FOR 'jeffrey'@'localhost' = PASSWORD('cleartext password'); -
update user
set password='[password]'('[newpassword]') where User='[user_name]' ; -
mysql command line args:
-
export text file with commands to rebuild all mysql tables:
mysqldump [databasename] > [dumpfilename.txt] -
restore from a dump:
mysql -u [username] -p < [dumpfilename.txt] -
dump entire database:
mysqldump -u [username] -p --opt [databasename] > [dumpfile.sql] -
restore from entire database dump:
mysql -u [username] -p --database=[databasename] < [dumpfile.sql] -
install using remi repo since other repos only had version 5.1 instead of 5.5
yum --enablerepo=remi install mysql-server mysql mysql-libs -
Config
sudo nano /etc/my.cnf -
Add performance settings under [mysqld]
query_cache_size=16M thread_cache_size=4 -
Start
sudo /sbin/chkconfig --levels 235 mysqld on sudo service mysqld start -
Auto Config
sudo /usr/bin/mysql_secure_installation -
Manual Config
* Login to MySQL
mysql -u root
* Change root password
USE mysql
SET PASSWORD FOR 'root'@'localhost' = PASSWORD('somesecret');
-Remove anonymous user and account without password
DELETE FROM user WHERE password = '';
DELETE FROM user WHERE user.user= '';
-Flush the privileges and drop test DB
FLUSH PRIVILEGES;
DROP DATABASE test;
-
Backup
mysqldump -u root -p --all-databases > ~/backup.sql http://sourceforge.net/projects/automysqlbackup/ -
Import
sudo mysql -u root -p < backup.sql
*Tuning
wget -O mysqltuner.pl mysqltuner.pl
wget --trust-server-names mysqltuner.pl
-
Automatically defragment
Mysqlcheck -o --user=root --password= -A -
Copy DB to Remote Server
mysqldump dbname -u root -pRootPassword | mysql --host=remotedb.us-east-1.rds.amazonaws.com --port=3306 --user=root -pRemoteRootPassword --database=remoteDbName -
Secure database to one user from command line
mysql -e "grant all privileges ON myDBname.* TO dbaccount@localhost IDENTIFIED BY 'mypassword';" --user=root --password=myrootpassword -
Troubleshooting
SHOW PROCESSLIST; show slow transactions mysqladmin ext -i1 | grep Threads_running
-
Install Memcached
yum install memcached -
show version
memcached –i -
Edit Config
sudo nano /etc/init.d/memcached -
Start
checkconfig memcached on service memcached start -
Install PHP Extension
yum install php54-pecl-memcache add the memcache extension to your php.ini file, usually at /etc/php.ini. extension=memcache.so
-
Install
sudo yum install git -
Generate key
ssh-keygen -t rsa -
Start a new git project:
git init -
Clone a git (target can be specified either locally or remotely, via any number of protocols):
git clone [target] -
Commit changes to a git:
git commit -m "[message]" -
Get info on current repository:
git status -
Show change log for current repository:
git log -
Update git directory from another repository:
git pull [target] -
Push branch to other repository:
git push [target] -
Create a new branch:
git branch [branchname] -
Switch to target branch:
git checkout [branchname] -
Delete a branch:
git branch -d [branchname] -
Merge two branches:
git merge [branchname] [branchname] -
Contributing
- Fork it
- Create your feature branch (git checkout -b my-new-feature)
- Commit your changes (git commit -am 'Add some feature')
- Push to the branch (git push origin my-new-feature)
- Create a new Pull Request
-
Branches
- Create a new branch (git branch my-new-feature)
- Switch to new branch (git checkout my-new-feature)
- Commit your changes (git commit -am 'Add some feature')
- Push to the branch (git push origin my-new-feature)
- Switch to master (git checkout master)
- Merge (git merge my-new-feature)
-
Ensure ssh-agent is enabled
eval "$(ssh-agent -s)" -
Add your SSH key to the ssh-agen
ssh-add ~/.ssh/id_rsa -
See file changes
git diff -
Git Post-Receive Hook on server
cat > hooks/postreceive #!/bin/sh GIT_WORK_TREE=/var/www/html export GIT_WORK_TREE do your stuff here chmod +x hooks/postreceive -
Add the remote repository to the local repository
git push website+master:refs/heads/master [FIRST TIME ONLY] git push website master [ALL OTHER TIMES] -
Add empty commit
git commit --allow-empty -
List all local branches
git branch -
List referenced remote branches
git branch -r -
Find which branches are already merged into master and can be removed
git checkout master git branch --merged -
Remove all outdated branches with:
git branch -d old-merged-feature -
Decide what to do with not merged branches
git branch --no-merged -
Creating a Fork and making Upstream PR
List the current configured remote repository for your fork.
git remote -vSpecify a new remote upstream repository that will be synced with the fork.
git remote add upstream https://github.com/ORIGINAL_OWNER/ORIGINAL_REPOSITORY.git -
Sync a fork
Fetch the branches and their respective commits from the upstream repository. Commits to master will be stored in a local branch, upstream/master
git fetch upstreamCheck out your fork's local master branch
git checkout masterMerge the changes from upstream/master into your local master branch. This brings your fork's master branch into sync with the upstream repository, without losing your local changes
git merge upstream/master -
Rebasing
First fetch the new master from the upstream repository, then rebase your work branch on that:
Option 1:
git fetch origin # Updates origin/master
git rebase origin/master # Rebases current branch onto origin/master
Option 2: Newer
git pull --rebase origin master
- Undo last commit
git reset --hard HEAD~1
- move last commit on master to different branch
git checkout -b feature/istio-elb-timeout
git merge master
git checkout master
git reset --keep HEAD~1 # Move master back
git checkout feature/istio-elb-timeout
git status
- move currently worked on files to a new branch
git stash
git checkout master
git pull
git checkout -b feature/new
git stash pop
The '.' in the jq '.' command above is the simplest jq "filter." The dot takes the input JSON and outputs it as is. You can read more about filters here, but the bare minimum to know is that .keyname will filter the result to a property matching that key, and [index] will match an array value at that index
$ USERX='{"name":"duchess","city":"Toronto","orders":[{"id":"x","qty":10},{"id":"y","qty":15}]}'
$ echo $USERX | jq '.'
And [] will match each item in an array:
echo $USERX | jq '.orders[].id'
"x"
"y"
Filtering output by value is also handy! Here we use | to output the result of one filter into the input of another filter and select(.qty>10) to select only orders with qty value greater than 10:
echo $USERX | jq '.orders[]|select(.qty>10)'
{
"id": "y",
"qty": 15
}
One more trick: filtering by key name rather than value:
$ ORDER='{"user_id":123,"user_name":"duchess","order_id":456,"order_status":"sent","vendor_id":789,"vendor_name":"Abe Books"}'
$ echo $ORDER | jq '.'
{
"user_id": 123,
"user_name": "duchess",
"order_id": 456,
"order_status": "sent",
"vendor_id": 789,
"vendor_name": "Abe Books"
}
$ echo $ORDER | jq 'with_entries(select(.key|match("order_")))'
{
"order_id": 456,
"order_status": "sent"
}
(cheat sheet version: with_entries(select(.key|match("KEY FILTER VALUE"))))
Check out more resources below to learn about other stuff jq can do!
-
Install
yum install rsync -
Sync from one server to another
sudo rsync -avz -e ssh root@prod.server.com:/var/www/server.com /var/www/
-
Install server monitor
rpm -Uvh http://yum.newrelic.com/pub/newrelic/el5/x86_64/newrelic-repo-5-3.noarch.rpm yum install newrelic-sysmond nrsysmond-config --set license_key=************ /etc/init.d/newrelic-sysmond start -
Install php agent
yum install newrelic-php5 newrelic-install install service httpd restart sudo nano newrelic.cfg license_key=REPLACE_WITH_REAL_KEY -
Start php agent
/etc/init.d/newrelic-daemon restart
-
Run deamon
celery multi start w1 -A myapplication --loglevel=info -
Run Flower in Supervisord
[program:flower] command=celery flower --broker=redis://localhost ; the program (relative uses PATH, can take args) process_name=%(program_name)s ; process_name expr (default %(program_name)s) numprocs=1 ; number of processes copies to start (def 1) autostart=true user=flower
-
Install
pip install supervisor -
Autoconfig
echo_supervisord_conf > /etc/supervisord.conf -
Example Config for Django app
[program:myapp] command=/usr/bin/gunicorn_django -w 4 -b 127.0.0.1:8000 directory=/home/ec2-user/django/application/app user=nobody autostart=true autorestart=true redirect_stderr=True -
Start Daemon
/usr/bin/supervisord -
Start Application
* usr/bin/supervisorctl supervisorctl {start,status,stop} hello
-
Reload Config
sudo /etc/init.d/nginx reload -
Test Config File
sudo /etc/init.d/nginx -t -
Worker processes
To take advantage of SMP and to enable good efficiency I would recommend changing this to read:
worker_processes 4; -
Max clients
You can work out the maximum clients value by multiplying this and the worker_processes settings:
max_clients = worker_processes * worker_connections -
Keepalive
The default is very high and can easily be reduced to a few seconds (an initial setting of 2 or 3 is a good place to start and you will rarely need more than that)
keepalive_timeout 0 # defaul: keepalive_timeout 65; -
Folder Permissions
As the default permissions only allow us, the 'demo' user, to browse our home folder, let's start off by giving Nginx access to this folder as well:
chmod 755 /home/demo mkdir -p /home/demo/public_html/domain1.com/{public,private,log,backup} -
Example Config for Django
server { listen 80; server_name example.org; access_log /var/log/nginx/example.log; location /media/ { # if asset versioning is used if ($query_string) { expires max; } } location /admin/media/ { # this changes depending on your python version root /path/to/test/lib/python2.6/site-packages/django/contrib; } location / { proxy_pass http://127.0.0.1:8000; proxy_set_header Host $host; proxy_set_header X-Real-IP $remote_addr; proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for; } } -
root
This is the key to serving static sites. If you are just trying to lay down some html and css, the root directive specifies the directory that you have stored your files in. I like to store my sites in /var/www, -
location
$uri is whatever someone typed after the domain name is $uri = /whatever. try_files will look in root directory for a file with a name matching the uri. if not, it will send to index.html Location takes two parameters, a string/regex and a block. The string/regex is a matcher for a specific location. So if you wanted anyone who went to example.com/ whatever to hit a specific page, you would use ‘whatever’ as the uri. Also note that this / uri will match all urls, since it’s treated as a regex. If you want a location block to match only an exact string, you can preface it with an equals sign, as shown below. But in this case, it’s ok for it to match all urls. location = / { ... } location / { try_files $uri $uri/ /index.html; } We can use another directive inside the block to serve a file called try_files. Try files takes a list of filenames or patterns that it will try to find in you root directory, and it will serve the first one it finds. For our simple static server, we want to try to find a file with the name of whatever comes after the slash, like ‘whatever.html’. If there is nothing after the slash, it should go for index.html. -
SSL
ssl on; listen 443 default ssl; ssl_certificate /etc/nginx/ssl_hostname.com/ssl-unified.crt; ssl_certificate_key /etc/nginx/ssl_hostname.com/ssl.key; -
Permissions for SSL Certs
Nginx's processes are laid out like this: - 1 nginx master process running as *root* - x nginx workers running as *www-data* Nginx's master process reads the SSL key, not the workers. Because of that, we can simply allow only root to read the private key -
Permissions for Files
One permission requirement that is often overlooked is a user needs x permissions in every parent directory of a file to access that file. Check the permissions on /, / home, /home/demo, etc. for www-data x access. My guess is that /home is probably 770 and www-data can't chdir through it to get to any subdir. If it is, try chmod o+x / home (or whatever dir is denying the request). To easily display all the permissions on a path, you can use namei -om /path/to/check -
To Enable services through firewall
sudo firewall-cmd --permanent --zone=public --add-service=http sudo firewall-cmd --permanent --zone=public --add-service=https sudo firewall-cmd --reload -
Auto start service
sudo systemctl enable nginx.service
-
Config File
/etc/syslog.conf -
Define where logs are sent
mail.* /var/log/maillog #defines where to send mail logs. use @@hostname to send to a remote host over tcp -
Send messages to Loggly over TCP using the template.
*.* @@logs-01.loggly.com:514;LogglyFormat
-
Commands
tmux ls = list sessions tmux new = new session tmux attach = attach to old session, keep existing sessions open tmux attach -b = attach to session, disconnect other connections tmux kill-session -
Keys
Ctrl-b-d = detach from current session Ctrl-b-n = creates new window Ctrl-b-0 = go to window 0 Ctrl-b-tab = toggle between windows Ctrl-b-c = create new window Ctrl-b-? = see bindings Ctrl-b-x = close current window/pane Ctrl-b-o = switch to other pane Ctrl-b-q = show panes Ctrl-b-V = new vertical pane Ctrl-b-arrow = switch panes Ctrl-b-[-arrow = scroll
- Run Playbook locally ansible-playbook -i "localhost," -c local
- finding Modules information:
ansible-doc -l -> to list out all modules ansible-doc -l | grep package -> to grep specific modules ansible-doc package -> to list out all information also >> ansible-doc -s yum -> also works for details of any modules
ansible all -m ping -o -> to display in single line if we are using sudo user then specify -s at the end to run cmd in sudo
hl - move L/R
jk - move up down
w - moves to start of next word
e - moves end of the word
b - begining of word
0 - begging of a line
$ - end of a line
2G- go to line 2. ( line #G)
/text - search with n and N
d - delete
dw - delete word
:w - save/write
:q
:q! - quit without save
u - undo
ctrl+r - redo
ctrl-b / ctrl-f - Move Backwards/Forward by Page
dd - delete/cut line
3dd - delete/cut 3 lines
4y - yank/copy 4 lines below
x - delete character
p - paste
/string Search forward for string
?string Search back for string
n Search for next instance of string
N Search for previous instance of string
wget https://github.com/prometheus/node_exporter/releases/download/0.11.0/node_exporter-0.11.0.linux-amd64.tar.gz
sudo mv node_exporter /usr/sbin/
sudo adduser prometheus -s /sbin/nologin
sudo nano /usr/lib/systemd/system/node_exporter.service
[Unit]
Description=Prometheus Node Exporter
After=network.target
[Service]
Type=simple
ExecStart=/usr/sbin/node_exporter -web.listen-address=:11402
Restart=on-abort
[Install]
WantedBy=multi-user.target
sudo systemctl enable node_exporter.service
sudo systemctl start node_exporter.service
First set timezone before logging
timedatectl list-timezones
sudo timedatectl set-timezone zone
timedatectl status
Logs since current boot
journalctl -b
To enable persistent logging:
sudo nano /etc/systemd/journald.conf
. . .
[Journal]
Storage=persistent
Show boots
journalctl --list-boots
Logs since jan
journalctl --since "2015-01-10" --until "2015-01-11 03:00"
journalctl --since 09:00 --until "1 hour ago"
journalctl --since yesterday
By unit
journalctl -u nginx.service -u php-fpm.service --since today
By Process ID
journalctl _PID=8088
By User ID
journalctl _UID=33 --since today
Truncate output
journalctl --no-full
journalclt --no-pager
Output to JSON
journalctl -b -u nginx -o json-pretty
See how much disk is being used
journalctl --disk-usage
Delete old logs
sudo journalctl --vacuum-size=1G
-
Create a service
sudo nano /etc/systemd/system/my.service sudo systemctl enable /etc/systemd/system/my.service sudo systemctl start my.service -
Edit Service Config
[Unit]
Description=My Service
Documentation=https://backplane.io/index
[Service]
TimeoutStartSec=0
ExecStart=/usr/local/bin/somecommand
[Install]
WantedBy=multi-user.target
WHERE is for rows: When querying, we can use the WHERE clause to filter the rows we get back. To use WHERE we specify a condition like “population less than 1000”:
SELECT *
FROM city
WHERE population < 1000;
SELECT is for Columns Conversely, if we want to get back only certain pieces of data (i.e. columns) of each row, we use SELECT:
SELECT name, countrycode
FROM city;
Both at the Same Time And the real power of SQL is that we can combine both together:
SELECT name, countrycode
FROM city
WHERE population < 1000;
multiple WHERE queries by using AND like:
WHERE population < 1000 AND countrycode = 'AIA'
JOIN
Actions like WHERE and SELECT act on a single table. We know how to get city data, but lifeexpectancy exists on the country table. How do we get them both together? The only way is to create one big table using JOIN. It connects city.countrycode to country.code. So for each city row, I take the city.countrycode and find the matching country.code row in the country table. Then I take those two rows and add them together. They are now one, larger row.
SELECT *
FROM city
JOIN country ON city.countrycode = country.code;
Using SELECT, WHERE and JOIN Create one big table with FROM and JOIN Pair down the rows with WHERE Pair down the columns with SELECT
SELECT city.name, country.lifeexpectancy
FROM city
JOIN country ON country.code = city.countrycode
WHERE country.lifeexpectancy > 80;
GROUP-BY Grouping in SQL is closer to a process of sorting, then squishing or flattening. SQL calls this flattening aggregation. Aggregation can take many forms. We’re about to simply count up the number of rows. Before we start grouping we need to decide which columns to flatten, and which columns to GROUP BY. Both types of columns go in the SELECT clause. For this query, we’re going to use countrycode and language.
Even with all this explanation, GROUP BY can remain a bit baffling. Let’s walk through it one more time step-by-step:
Start with the full, ungrouped table. Sort all the rows together based on the GROUP BY columns. So in our example: move all the USA rows together, and then all the TUV rows, and so on. For each group All of the columns specified in the GROUP BY clause are already the same so they simply collapse down into that value. For the other columns, they get combined based on the aggregate function. In our case, we COUNT each row that exists and display the final number.
SELECT
countrycode,
COUNT(language)
FROM countrylanguage
GROUP BY countrycode;
Multiply Two Columns:
Our database has a table named purchase with data in the following columns: id, name, price, quantity, and discount_id. Let’s multiply the price by the quantity of the products to find out how much you paid for each item in your order.
SELECT
name
price*quantity AS total_price
FROM purchase;
Multiplying from Other Columns
You can also use data from two columns coming from different tables. We have another table in our database named discount that has columns named id and value; the latter represents the percent discount on the item with the given ID.
SELECT
p.name,
p.price*p.quantity*(100-d.value)/100 AS total_price
FROM purchase p
JOIN discount d ON d.id=p.discount_id;
import CSV data with a single command, the table is created automatically:
> .import --csv city.csv city
> select count(*) from city;
1117
Data could be exported as SQL, CSV, JSON, even Markdown and HTML. Takes just a couple of commands:
.mode json
.output city.json
select city, foundation_year, timezone from city limit 10;
.shell cat city.json
Read json
select
json_extract(value, '$.iso.code') as code,
json_extract(value, '$.iso.number') as num,
json_extract(value, '$.name') as name,
json_extract(value, '$.units.major.name') as unit
from
json_each(readfile('currency.sample.json'))
;
Reference: https://github.com/jorgebucaran/fish-cookbook/blob/master/README.md
Only show abbreviated paths
set fish_prompt_pwd_dir_length 0Find command status
echo $statusFish shebang
#!/usr/bin/env fish
Set variable
set foo 42
The set builtin accepts the following flags to explicitly declare the scope of the variable:
-l, --local: available only to the innermost block -g, --global: available outside blocks and by other functions -U, --universal: shared between all fish sessions and persisted across restarts of the shell -x, --export: available to any child process spawned in the current session
Export variable
set -x foo 42
Show all vars
set
Set path persistently
set -U fish_user_paths $fish_user_paths my_path
Unset path persistently
if set -l index (contains -i $my_path $PATH)
set -e PATH[$index]
end
Make a function
To make this function available in future fish sessions save it to ~/.config/fish/functions/mkdirp.fish. Note: function name and file name should match
function mkdirp
mkdir -p $argv
end
or funsave
funcsave mkdirp
How do I access the arguments passed to a function in fish? Use the $argv variable.
function Foo
printf "%s\n" $argv
end
How do I parse command line arguments in fish? Use a for loop.
for option in $argv
switch "$option"
case -f --foo
case -b --bar
case \*
printf "error: Unknown option %s\n" $option
end
end
Where's the .bash_profile or .bashrc equivalent in fish?
Your fish configuration is saved to ~/.config/fish/config.fish.
To read a file line by line, use the read builtin.
while read -la line
echo $line
end < my_file
How do I read from stdin in fish? Use the read builtin.
read --prompt "echo 'Name: ' " -l name
Redirect stderr to $my_file.
my_command 2> $my_fileRedirect stdout to $my_file.
my_command > $my_fileRedirect stdout to stderr.
my_command >&2Redirect stderr to stdout.
my_command 2>&1- Basics
[\^$.|?*+() # special characters any other will match themselves
\ # escapes special characters and treat as literal
* # repeat the previous item zero or more times
. # single character except line break characters
.* # match zero or more characters
^ # match at the start of a line/string
$ # match at the end of a line/string
.$ # match a single character at the end of line/string
^ $ # match line with a single space
^[A-Z] # match any line beginning with any char from A to Z
* The ^ (caret) fixes your pattern to the beginning of the line. For example the pattern ^1 matches any line starting with a 1.
* The $ (dollar) fixes your pattern to the end of the sentence. For example, 9$ matches any line ending with a 9.
To use it, replace the libx264 codec with libx265, and push the compression lever further by increasing the CRF value — add, say, 4 or 6, since a reasonable range for H.265 may be 24 to 30. Note that lower CRF values correspond to higher bitrates, and hence produce higher quality videos.
mp4 to lower output
ffmpeg -i input.mp4 -vcodec libx265 -crf 28 output.mp4
Mov to mp4
ffmpeg -i my-video.mov -vcodec h264 -acodec mp2 my-video.mp4
Install
brew install gnupg
Generate key
gpg --gen-key
Export your public key on your second computer into an armored blob using the email address you chose when creating the key
gpg --export --armor -email > pubkey.asc
Export your public key using the name on the key and base64 encode
gpg --export "firstname lastname" | base64
Import another users public key
gpg --import pubkey.asc
Show keys on keyring
gpg --list-keys
Encrypt a file using someone elses public key
gpg --encrypt --recipient "Cory Heath" myriad.pdf
Decrypt file
gpg --decrypt myriad.pdf.gpg > myriad.pdf
Init
ipfs init
ipfs daemon
To upload to IPFS, all we need to do on our first computer is
ipfs add myriad.pdf.gpg
make sure our file is available on IPFS
ipfs pin ls
download the posted encrypted file from your first computer from IPFS using the same hash:
ipfs get QmYqSCWuzG8Cyo4MFQzqKcC14ct4ybAWyrAc9qzdJaFYTL
Install
sudo apt update && sudo apt install dnsutils #debian
sudo yum install bind-utils #centos
Query the linux.org domain:
dig linux.org
The first line of the output prints the installed dig version, and the queried domain name. The second line shows the global options (by default, only cmd).
; <<>> DiG 9.13.3 <<>> linux.org
;; global options: +cmd
If you don’t want those lines to be included in the output, use the +nocmd option. This option must be the very first one after the dig command.
The next section includes technical details about the answer received from the requested authority (DNS server). The header shows the opcode (the action performed by dig) and the status of the action. In this example, the status is NOERROR, which means that the requested authority served the query without any issue.
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 37159
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 2, ADDITIONAL: 5
This section can be removed using the +nocomments option, which also disables some other section’s headers.
The “OPT” pseudo section is shown only in the newer versions of the dig utility. You can read more about the Extension mechanisms for DNS (EDNS) here .
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
To exclude this section from the output, use the +noedns option.
In the “QUESTION” section dig shows the query (question). By default, dig requests the A record.
;; QUESTION SECTION:
;linux.org. IN A
You can disable this section using the +noquestion option.
The “ANSWER” section provides us with an answer to our question. As we already mentioned, by default dig will request the A record. Here, we can see that the domain linux.org points to the 104.18.59.123 IP address.
;; ANSWER SECTION:
linux.org. 300 IN A 104.18.59.123
linux.org. 300 IN A 104.18.58.123
Usually, you do not want to turn off the answer, but you can remove this section from the output using the +noanswer option.
The “AUTHORITY” section tells us what server(s) are the authority for answering DNS queries about the queried domain.
;; AUTHORITY SECTION:
linux.org. 86379 IN NS lia.ns.cloudflare.com.
linux.org. 86379 IN NS mark.ns.cloudflare.com.
You can disable this section of the output using the +noauthority option.
The “ADDITIONAL” section gives us information about the IP addresses of the authoritative DNS servers shown in the authority section.
;; ADDITIONAL SECTION:
lia.ns.cloudflare.com. 84354 IN A 173.245.58.185
lia.ns.cloudflare.com. 170762 IN AAAA 2400:cb00:2049:1::adf5:3ab9
mark.ns.cloudflare.com. 170734 IN A 173.245.59.130
mark.ns.cloudflare.com. 170734 IN AAAA 2400:cb00:2049:1::adf5:3b82
The +noadditional option disables the additional section of a reply.
The last section of the dig output includes statistics about the query.
;; Query time: 58 msec
;; SERVER: 192.168.1.1#53(192.168.1.1)
;; WHEN: Fri Oct 12 11:46:46 CEST 2018
;; MSG SIZE rcvd: 212
You can disable this part with the +nostats option.
Printing Only the Answer Generally, you would want to get only a short answer to your dig query.
- Get a Short Answer To get a short answer to your query, use the +short option:
dig linux.org +short
104.18.59.123
104.18.58.123
The output will include only the IP addresses of the A record.
- Get a Detailed Answer
For more a detailed answer, turn off all the results using the +noall options and then turn on only the answer section with the +answer option.
dig linux.org +noall +answer
; <<>> DiG 9.13.3 <<>> linux.org +noall +answer
;; global options: +cmd
linux.org. 67 IN A 104.18.58.123
linux.org. 67 IN A 104.18.59.123
Query Specific Name Server By default, if no name server is specified, dig uses the servers listed in /etc/resolv.conf file.
To specify a name server against which the query will be executed, use the @ (at) symbol followed by the name server IP address or hostname. For example, to query the Google name server (8.8.8.8) for information about the linux.org domain you would use:
dig linux.org @8.8.8.8
; <<>> DiG 9.13.3 <<>> linux.org @8.8.8.8
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 39110
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 0, ADDITIONAL: 1
;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 512
;; QUESTION SECTION:
;linux.org. IN A
;; ANSWER SECTION:
linux.org. 299 IN A 104.18.58.123
linux.org. 299 IN A 104.18.59.123
;; Query time: 54 msec
;; SERVER: 8.8.8.8#53(8.8.8.8)
;; WHEN: Fri Oct 12 14:28:01 CEST 2018
;; MSG SIZE rcvd: 70
Query a Record Type Dig allows you to perform any valid DNS query by appending the record type to the end of the query. In the following section, we will show you examples of how to search for the most common records, such as A (the IP address), CNAME (canonical name), TXT (text record), MX (mail exchanger), and NS (name servers).
- Querying A records To get a list of all the address(es) for a domain name, use the a option:
dig +nocmd google.com a +noall +answer
google.com. 128 IN A 216.58.206.206
As you already know, if no DNS record type is specified, dig will request the A record. You can also query the A record without specifying the a option.
- Querying CNAME records To find the alias domain name use the cname option:
dig +nocmd mail.google.com cname +noall +answer
mail.google.com. 553482 IN CNAME googlemail.l.google.com.
- Querying TXT records Use the txt option to retrieve all the TXT records for a specific domain:
dig +nocmd google.com txt +noall +answer
google.com. 300 IN TXT "facebook-domain-verification=22rm551cu4k0ab0bxsw536tlds4h95"
google.com. 300 IN TXT "v=spf1 include:_spf.google.com ~all"
google.com. 300 IN TXT "docusign=05958488-4752-4ef2-95eb-aa7ba8a3bd0e"
- Querying MX records To get a list of all the mail servers for a specific domain use the mx option:
dig +nocmd google.com mx +noall +answer
google.com. 494 IN MX 30 alt2.aspmx.l.google.com.
google.com. 494 IN MX 10 aspmx.l.google.com.
google.com. 494 IN MX 40 alt3.aspmx.l.google.com.
google.com. 494 IN MX 50 alt4.aspmx.l.google.com.
google.com. 494 IN MX 20 alt1.aspmx.l.google.com.
- Querying NS records To find the authoritative name servers for our specific domain use the ns option:
dig +nocmd google.com ns +noall +answer
google.com. 84527 IN NS ns1.google.com.
google.com. 84527 IN NS ns2.google.com.
google.com. 84527 IN NS ns4.google.com.
google.com. 84527 IN NS ns3.google.com.
- Querying All Records Use the any option to get a list of all DNS records for a specific domain:
dig +nocmd google.com any +noall +answer
google.com. 299 IN A 216.58.212.14
google.com. 299 IN AAAA 2a00:1450:4017:804::200e
google.com. 21599 IN NS ns2.google.com.
google.com. 21599 IN NS ns1.google.com.
google.com. 599 IN MX 30 alt2.aspmx.l.google.com.
google.com. 21599 IN NS ns4.google.com.
google.com. 599 IN MX 50 alt4.aspmx.l.google.com.
google.com. 599 IN MX 20 alt1.aspmx.l.google.com.
google.com. 299 IN TXT "docusign=05958488-4752-4ef2-95eb-aa7ba8a3bd0e"
google.com. 21599 IN CAA 0 issue "pki.goog"
google.com. 599 IN MX 40 alt3.aspmx.l.google.com.
google.com. 3599 IN TXT "facebook-domain-verification=22rm551cu4k0ab0bxsw536tlds4h95"
google.com. 21599 IN NS ns3.google.com.
google.com. 599 IN MX 10 aspmx.l.google.com.
google.com. 3599 IN TXT "v=spf1 include:_spf.google.com ~all"
google.com. 59 IN SOA ns1.google.com. dns-admin.google.com. 216967258 900 900 1800 60
Reverse DNS Lookup To query the hostname associated with a specific IP address use the -x option. For example, to perform a reverse lookup on 208.118.235.148 you would type:
dig -x 208.118.235.148 +noall +answer
As you can see from the output below the IP address 208.118.235.148 is associated with the hostname wildebeest.gnu.org.
; <<>> DiG 9.13.3 <<>> -x 208.118.235.148 +noall +answer
;; global options: +cmd
148.235.118.208.in-addr.arpa. 245 IN PTR wildebeest.gnu.org.
- Download and Install
https://github.com/FiloSottile/age
- Generate a New Key Par
mkdir ~/.age
age-keygen -o ~/.age/key.txt
Share the public key with recipient
- Encrypt a file with recipient's public key
age -r [receipient public key] example.txt > example.txt.age
- Decrypt a file
age --decrypt example.txt.age -i ~/.age/key.txt -o example.txt
- Encrypt & Decrypt using a passphrase
# encrypt
age -p secrets.txt > secrets.txt.age
Enter passphrase (leave empty to autogenerate a secure one):
# decrypt
$ age -d secrets.txt.age > secrets.txt
Enter passphrase:
- Install
git clone https://github.com/asdf-vm/asdf.git ~/.asdf --branch v0.7.8
$ mkdir -p ~/.config/fish/completions; and cp ~/.asdf/completions/asdf.fish ~/.config/fish/completions
## edit config.fish
# asdf
source $HOME/.asdf/asdf.fish
- Pyenv replacement
$ asdf plugin add python
$ asdf install python latest:3 # At the moment of writing this, it installed 3.8.4
$ asdf global python 3.8.4 # This sets python 3.8.4 as our default python version
- Rbenv
$ asdf plugin add ruby
$ asdf install ruby latest # We can omit the version number. Currently installs 2.7.1
$ asdf global ruby 2.7.1
- Goenv
$ asdf plugin add golang
$ asdf install golang latest # 1.14.6
$ asdf global golang 1.14.6
- Nvm
$ asdf plugin add nodejs
$ asdf install nodejs 12.18.2
$ asdf global nodejs 12.18.2
- Asdf Global
Using asdf global creates a file under your HOME directory called .tool-versions. This lets asdf know which versions to use. And of course, in contrast to global, there is also the local keyword that creates another .tool-versions. This is useful when projects require different version.
$ cat ~/.tool-versions
python 3.8.4
ruby 2.7.1
golang 1.14.6
nodejs 12.18.2
- Extras
In order to accommodate my work flow when I was still using pyenv virtualenv, I created a function that behaves quite similar to pyenv virtualenv.
$ touch ~/.config/fish/functions/venv.fish
function venv --argument-names 'python_version' --description 'Create virtualenv named the same as current directory'
set -l python_bin
if not test -n "$python_version"
# Use default python version set by asdf
set python_bin ($HOME/.asdf/bin/asdf which python)
else
set python_bin $ASDF_DIR/installs/python/$python_version/bin/python
end
set -l venv_name (basename $PWD | tr . -)
echo
if not test -e $python_bin
echo "Python version `$python_version` is not installed."
return 1
end
echo Creating virtualenv `$venv_name`
$python_bin -m venv $HOME/.virtualenvs/$venv_name
source $HOME/.virtualenvs/$venv_name/bin/activate.fish
end
Whenever I’m inside a python project, I just need to type venv or venv <python_version> and it will automatically create a virtualenv under ~/.virtualenvs using the current directory name.
In order to automatically activate the virtualenv when cding to a project, do the following:
$ touch ~/.config/fish/conf.d/__auto_venv.fish
function __auto_venv --on-variable PWD --description "Automatically activate python venv"
set -l venv_name (basename $PWD | tr . -)
if test -d $HOME/.virtualenvs/$venv_name
source $HOME/.virtualenvs/$venv_name/bin/activate.fish
end
end
Luckily Terraform allows for plugins caching. So, whenever plugin has to be downloaded and is present in the cache directory, it will be copied into the project instead. This can save some time and bandwidth.
touch ~/.terraformrc
Put this in your ~/.terraformrc and enjoy:
plugin_cache_dir = "$HOME/.terraform.d/plugin-cache"
Then create the cache directory:
mkdir -p $HOME/.terraform.d/plugin-cache