➖Linux Utilities

This page demonstrates some of the most used Linux command line utilities and their usage.

Parallel Processing

parallel

Process Linux commands in parallel. Single-instance execution is time-consuming. Some examples where parallel command can be leveraged:

• file sizes in a directory

• Deleting files

#To get the sizes of objects 
parallel -j 20 du -sh ::: *

#To remove directories in parallel
parallel -j 20 rm -rf ::: *

#use find max depth 2 and parallel utils
find . -max-depth 2 -type d | parallel -j 10 rm -rf ::: {}

pixz

pixz is a parallel compression tool. It compresses huge files in less time using parallel execution. It uses xz compression.

# Compress huge files parallelly
tar --owner=root --group=root -cf - . |  pixz >  ../<your>.tar.xz

flock

Manage locks from shell scripts. It can be used to ensure that only one process of a command is running at a time. This is particularly useful in situations where multiple processes may be trying to execute the same command simultaneously, and you want to ensure that only one of them succeeds.

flock <path to .lock> --command my-command

Process Management

kill

kill is a command utility for handling process ops. It is important to clean up all processes invoked by the parent process, or else it leads to zombie processes. Users have to explicitly kill the child processes before termination.

# Kill process
kill -9 <pid>

# Send SIGTERM to a process
kill -15 <pid>

# Kill all child process
kill -9 -- -GPID

nohup

nohup (No Hang Up) is a command in Linux systems that runs the process even after logging out from the shell/terminal.

nohup command [command-argument ...]

Misc

fakeroot

Imagine that you are a developer/package maintainer, etc. working on a remote server. You want to update the contents of a package and rebuild it, download and customize a kernel from kernel.org and build it, etc. While trying to do those things, you'll find out that some steps require you to have root rights (UID and GID 0) for different reasons (security, overlooked permissions, etc). But it is not possible to get root rights, since you are working on a remote machine (and many other users have the same problem as you). This is what exactly fakeroot does: it pretends an effective UID and GID of 0 to the environment which requires them.

$ fakeroot
# echo "Wow I have root access" > root.tst
# ls -l root.tst
-rw-rw-r-- 1 root root   23 Oct 25 12:13 root.tst
# ls -l /root
ls: cannot open directory /root: Permission denied
# exit
$ ls -l root.tst
-rw-rw-r-- 1 ubuntu ubuntu 23 Oct 25 12:13 root.tst