Useful commands and scripts for sysadmin basic tasks.
Optional line arguments are surronded by square brackets [], and example arguments are surrondend by <>.
Configuration file /etc/ssh/sshd_config
- 'Port' - Default SSH port (Change)
- 'PermitRootLogin' - Root login allowed ways (Change from 'yes' to 'without-password' to only allow root connection with public key authentication)
Commands to list, add and remove rules on Iptables program.
$ iptables -S
$ iptables -nL --line-numbers
$ iptables -I <INPUT [line-number] -p tcp -m tcp --dport 80 -j ACCEPT>
$ iptables -D <INPUT -i lo -j ACCEPT>
To persist the Iptables modified rules, I use iptables-persistent utilitary. After change a rule, just exec invoke-rc.d iptables-persistent save to save modifications.
My common Iptables configuration:
Command-line tool for transferring data using various protocols
- Create
curl-format.txtfile:
time_namelookup: %{time_namelookup}\n
time_connect: %{time_connect}\n
time_appconnect: %{time_appconnect}\n
time_pretransfer: %{time_pretransfer}\n
time_redirect: %{time_redirect}\n
time_starttransfer: %{time_starttransfer}\n
----------\n
time_total: %{time_total}\n
- Make the request:
curl -w "@curl-format.txt" -o /dev/null -s "http://wordpress.com/"
- Create
body_requestfile:
<?xml version="1.0" encoding="UTF-8"?>
<soapenv:Envelope xmlns:soapenv="http://schemas.xmlsoap.org/soap/envelope/" xmlns:wse="NameSpace">
<soapenv:Header/>
<soapenv:Body>
...
</soapenv:Body>
</soapenv:Envelope>
- Make the request:
$ curl -X POST -H "Content-Type: text/xml" -H "SOAPAction: MYSoapAction" --data-binary @body_request.xml https://my.server.com/Path
Print network connections
List tcp connections (t), without resolving ip addresses (n) and showing the process pid (p). To show the process pid (p) you may need to run as root.
$ netstat -tnp
- Useful tips:
Filter by port
$ netstat -tnp | grep :80
Network mapping. Scan hosts or IP address. Along with many purposes, nmap can be used to scan open ports in a remote host.
Scan a host or IP address. Use -6 to scan an IPv6 address
$ nmap [-6] host_or_address
Scan multiple IP address or subnet (IPv4)
$ nmap 192.168.1.1 192.168.1.2 192.168.1.3
## works with same subnet i.e. 192.168.1.0/24
$ nmap 192.168.1.1,2,3
IPv6 could take years to scan a normal subnet /64. Use with caution.
Scan IPs from a file
$ nmap -iL /tmp/address_list.txt
Turn on OS detection
# IPv4
$ nmap -A 192.168.1.1
# IPv6
$ nmap -A -6 ::1
Scan a host for UDP services (UDP scan)
$ nmap -sU 192.168.1.1
Get process stats
$ ps -aux | grep <proc-name>
Column order:
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
Basic commands to handle user attributes (Passsword, groups, etc):
$ adduser <username>
$ adduser <username> <group>
$ useradd <username>
$ passwd <username>
$ deluser <username>
Auditing commands:
$ w
$ last
$ last -f /var/log/wtmp.1 (ls /var/log/wtmp*)
$ lastlog
List which user/process has opened a specific file
$ lsof /var/log/syslog
Run as root to show process owned by root.
Commands for listing system services:
$ service --status-all
$ initctl list
Useful tools
- vim - Text editor
- htop - Interactive process viewer