Comprehensive Linux Guide: Filesystem, Commands, Permissions, Users, Processes, and Software Installation

Linux Filesystem

The Linux filesystem contains several standard directories:

/var : variable files such as logs, spools, and temporary files.

/home : each user’s personal files and configuration.

/proc : virtual files that expose kernel and process information.

/bin : essential binary executables available to all users.

/etc : system configuration files.

/root : home directory of the superuser.

/dev : device files representing hardware and virtual devices.

Linux Command Operations

Show current directory: pwd

Change directory: cd , cd [directory] , cd ~ , cd .. , cd - , cd /

List files: ls , ls -l , ls -a , ls -la

Create directories: mkdir [name] , mkdir -p path/to/dir

Remove directories: rmdir [name] , rmdir -p [path]

Remove files/directories: rm -rf [target] , rm -ri [target]

Copy files/directories: cp -r src dest , cp -ri src dest

Move/rename: mv src dest

Create empty file: touch filename

View/edit files: vi filename (command, insert, and last‑line modes described below)

Display file content: cat filename , cat > filename

Show file head: head -n N filename

Show file tail: tail filename , tail -f filename , tail -n N filename

vi Editor Modes

Mode

Description

Command mode

Enter commands such as

dd

,

ndd

to delete lines.

Insert mode

Enter text; exit with

Esc

.

Last‑line mode

Enter with

Esc :

to save/quit (

:wq!

) or force quit (

:q!

).

Linux Permission Management

Linux defines three basic permissions—read ( r ), write ( w ), and execute ( x )—for owner, group, and others. Example output of ls -l :

drwxr-xr-x 2 root root 4096 Sep 23 2011 bin

d : directory

rwx : owner permissions

r-x : group permissions

r-x : others permissions

Change permissions with chmod :

chmod [options] [mode] file

Option

Description

-c

Show changes

-f

Suppress errors

-R

Recursive

-v

Verbose output

Two ways to specify the mode:

Symbolic: chmod u=rwx,g=rw,o=rw file

Numeric: chmod 753 file (owner 7=rwx, group 5=r-x, others 3=-wx)

Linux Process Management

View running processes with ps and filter with grep :

[shang@localhost ~]$ ps -ef | grep sshd
root   1829  1  0 May24 ?   00:00:00 /usr/sbin/sshd
shang 24166 24100 0 20:17 pts/2 00:00:00 grep sshd
[shang@localhost ~]$

Terminate a misbehaving process using kill -9 PID .

Linux Common Commands

clear : clear the terminal screen.

man : view manual pages for commands.

mnt : mount filesystems.

SSH service control: service sshd start , service sshd restart , service sshd stop .

Run a JAR in background: nohup java -jar jar-0.0.1-SNAPSHOT.jar & .

Linux Software Installation

Three primary installation methods:

tar : extract .tar , .tar.gz , or .tar.bz2 packages.

rpm : Red Hat package manager, install with rpm -ivh package.rpm .

yum : resolves dependencies and downloads RPMs automatically.

Installation Commands

Extract archives: tar -zxvf archive.tar.gz # gzip tar -jxvf archive.tar.bz2 # bzip2 tar -xvf archive.tar # plain tar

RPM operations: rpm -qa | grep keyword # list installed packages rpm -e package.rpm # uninstall rpm -ivh package.rpm # install with progress rpm -Uvh package.rpm # upgrade