Essential Commands
apropos list => find existing commands
CMD + A => move to start
CMD + E => move to end
CMD + U => delete to the start of the line
CMD + K => delete to the end of the line
CTRL - R => search in command history
CTRL - C => cancel the command
Linux File System
/bin => binary files
/boot => boot loader and kernel
/dev => device files
/etc => configuration files
/home => user home directory
/lib => library files
/media => temporarily mounted storage
/opt => optional installed software
/proc => kernel processes
/root => root user home folder
/run => information about running processes
/src => files served by device like NFS
/sys => information about system hardware
/tmp => temporary data
/usr => another location for software
File System Operations
ls -R path => recursively print content in a directory
ls -l => show list with info
mkdir -p => create whole path
Creating Links
ln -s filename linkname => create symbolic link
ln filename linkname => create hard link (same size)
file => show file type for links
Finding Files
find . -name apple => search in current directory
find . -name *apple* => search using glob
find . -size -10M => find files smaller than 10 MB
find . -size +10M => find files larger than 10 MB
Outputs and Redirects
- Standard input (stdin) - 0
- Standard output (stdout) - 1
- Standard error (stderr) - 2
- Redirect output:
ls 1> output.txt - Redirect error:
ls 2> output.txt - Append to file:
echo 'some text' >> file.txt
File Comparisons
diff -u file1 file2 => show differences (git format)
cmp file1 file2 => compare binary files
cmp -l file1 file2 => show list of differences
hexdump file1 => display hexadecimal representation
stat file1 => show file metadata
Archiving and Compression
tar -cvf archive.tar folder => create an archive
tar -xf archive.tar => extract archive
tar -tf archive.tar => list archive contents
zip -R archive.zip folder => zip a folder
unzip archive.zip => unzip a folder
Security and Administration
File Permissions
chmod => change permission mode
chown, chgrp => change file owner and group
| Role | Read (4) | Write (2) | Execute (1) | Result |
|---|---|---|---|---|
| User | R | W | X | 7 (rwx) |
| Group | R | - | X | 5 (rx) |
| Others | R | - | - | 4 (r) |
vim /etc/sudoers => check users with sudo privileges
Software Management
apt update => update package index
apt upgrade => install updates
apt search package => search for packages
apt remove package => uninstall software
Remote Access and File Transfers
sftp root@ip => connect via SFTP
scp user@host:path-to-file => copy file to remote host
System Operations
Boot Process and Startup
shutdown -r now => restart system
shutdown -h +5 => shutdown in 5 minutes
shutdown -c => cancel shutdown
- GRUB bootloader loads the kernel.
- Kernel mounts the root file system.
- System boots to the configured target.
systemctl isolate reboot.target => reboot using targets
systemctl set-default rescue.target => boot into rescue mode
systemctl set-default graphical.target => restore GUI mode
Process and Service Management
systemctl => list all services
systemctl start|stop service => start or stop service
systemctl disable service => prevent service from starting at boot
Kernel Management
uname -r => show kernel version
dpkg -i kernel_package.deb => update kernel
System Monitoring
df -h => check disk usage
free -h => check memory usage
cat /proc/cpuinfo => CPU information
Scheduling Tasks
- Cron: Best for always-on machines.
- Anacron: Best for systems that sleep.
cat /etc/crontab => list cron jobs
cat /etc/anacrontab => list anacron jobs
Disaster Recovery
- Backup data and configurations regularly.
- Test backups to ensure reliability.
- Store backups in multiple locations.
- Consider off-site replication.
Conclusion
This post covers Linux administration essentials, including file system operations, security management, system monitoring, and automation. Mastering these topics ensures effective Linux system management and troubleshooting.