Linux Pocket Guide

Tldr

Sharing my reading notes from the book Linux Pocket Guide by Daniel J. Barrett. Check out them for practical takeaways to improve your Linux skills!

Getting help

Command	Utility
man wc
man -k database | less	Search by keyword
info ls
wc --help	Many Linux commands respond to the option --help

• If the output is longer than the screen, pipe it into the less program to display it in pages.
• Your friend, the echo command: echo My name is $USER.

Linux: A first view

• Linux has four major parts:

  1. The kernel
  2. Supplied programs
  3. The shell
  4. X

• To determine the version of the Linux operating system:

  • cat /etc/*release
  • uname -a
  • hostnamectl

• In Linux, all files and directories descend from the root (/).

• There are several ways to locate or refer to your home directory:

  • cd with no arguments
  • $HOME variable
  • ~

Directory	Description
/usr/sbin	Programs (usually binary files) intended to be run by the superuser
/etc	Configuration files for the system (and other miscellaneous stuff)
/dev	Device files for interfacing with disks and other hardware
/var	Files specific to this computer, created and updated as the computer runs
/proc	Operating system state

• Files in /proc are used mostly by programs, but feel free to explore them.
  • cat /proc/version
• To see the ownership and permissions of a directory, add the -d option.
  • ls -ld mydir
  • -rwxr-x--- means a file (-) that can be read (r), written (w), and executed (x) by the owner, read and executed by the group, and not accessed at all by other users.
• To see who’s logged into the computer, type who.
• To change password of current user, type passwd.
• To display hostname of the system, type hostname.
• To list all processes sorted by their current system resource usage, type top.

Shell features

• Use type command to tell a command is a shell builtin or a program.
• Use export command to make a variable and its value available to other programs.
• To run a sequence of commands, but stop execution if any of them fails, separate them with && symbols.
  • command1 && command2 && command3
• Single quotes treat their contents literally, while double quotes let shell constructs be evaluated.
  • Backquotes cause their contents to be evaluated as a shell command.
  • A dollar sign and parentheses are equivalent to backquotes.
• A job is simply the shell’s unit of work.
  • Jobs are at a higher level than Linux processes, the Linux operating system knows nothing about them.
  • Type ^Z in a shell, while a job is running in the foreground, will suspend that job. It simply stops running, but its state is remembered.
    • Now you’re ready to type bg to put the command into the background, or fg to resume it in the foreground. You could also leave it suspended and run other commands.
  • Type ^C to kill a command running in the foreground immediately.
  • Type ^D to terminate a shell, either run the exit command.

who | wc -l
echo $SHELL
PATH=$PATH:/usr/sbin
echo $PATH
type who
export MYVAR=3
printenv HOME
echo This year is `date +%Y`
echo This year is $(date +%Y)
history 10
history -c # Clear (delete) your history
jobs
bg %2

File operations

• Use ls to list files in a directory.

  • The -a option displays all files
  • The -l option produces a long listing
  • The -S option sorts files by their size
  • The -t option sorts files by the time they were last modified

• Use cp to copy a file.

  • The -a or -r option for recursively copying directories

• Use cat to view files in their entirety.

• Use less to view text files one page at a time.

• Use head to view the first lines of a text file.

• Use tail to view the last lines of a text file.

find /var/www -name '*.css' # find files by name
grep font /var/www/html/style.css # find files containing text
grep -R font /var/www/html/ # grep recursively for a directory