Init

A collection of useful linux commands and other stuff.

ngrep

OS X: brew install ngrep

ngrep -d en1 -q -W byline "GET"

Exclude using grep

Exclude matching string using grep. Use v argument with grep.

tail -f access.log | grep -v 'HEAD'

This will exclude all the HEAD requests from access.log file.

Find the pid of a process by name

pgrep celery

sshconfig

~/.ssh/config - Create this file if doesn't exist.

Add the following contents

Host dev-machine
    HostName dev.example.com
    Port 22
    User apps

You can invoke ssh as ssh dev-machine

Pgrep and kill the process with a single command

pgrep flower | xargs kill

Run a command in background with a single command

flower -A blog &

& sends the job to background.

You can check the background jobs using jobs

Fuser (Linux)

The fuser command is a very smart unix utility used to find which process is using a file, a directory or a socket. It also gives information about the user owning the process and the type of access. The fuser tool displays the process id(PID) of every process using the specified files or file systems.

fuser -n tcp 80

Lists all the processes that are using port 80.

lsof -i tcp:3000 (OS X)

List the pids of the process listening on port 3000.

lsof -i tcp:3000

To only display the pid's use the terse option.

lsof -t -i tcp:3000

Also another usage

lsof -i :3000

strace (Linux) or dtruss (OS X)

strace It intercepts and records the system calls which are called by a process and the signals which are received by a process. The name of each system call, its arguments and its return value are printed on standard error or to the file specified with the -o option.

strace -p 1234

strace to find out all open system calls

strace -e open bash

List all the files opened by a process

ls /proc/30880/fd

where 30880 is the PID.

/dev/pts (Linux)

> tty
/dev/pts/0

Switch to another console.

echo "Hello World !" > /dev/pts/0

The text "Hello World !" would be printed in the first terminal.

Come out of a broken ssh session.

Press Enter ~ .

Compare and generate a diff between 2 directories

diff -ru dir1/ dir2

For just the files that have changes

diff -rqu dir1/ dir2

Create a named pipe

mkfifo my_pipe

This is similar to shell pipe | but uses a file instead.

Display the env variables of a running process

Source

xargs --null --max-args=1 < /proc/self/environ

Print the current tty

The tty command returns the filename of the terminal connected to standard input

tty

Get the PID of the current shell

echo $$

Go back to the previous directory in bash shell

cd -

Change the shell for an user

usermod -s /bin/bash <username>

chsh -s /bin/bash

List all the directories with their size

sudo du -hs *

List all the files with their size

sudo du -h .

OS X device block size

diskutil info / | grep "Block Size"

OS X file system block size

stat -f %k .

Get distro info on linux

cat /etc/issue

iotop

Input/Output stats

Clear bash cmd location hash

The following will clear where bash thinks fab is located:

hash -d fab

This command updates the shell's hash of locations of commands