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