Linux Commands
1. Navigation and Basic Commands
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Navigation:
pwd– Print the current working directory.cd– Change directory.cd /– Go to the root directory.cd -– Go to the previous directory.cd ~– Go to the home directory.
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Listing Files:
ls– List files and directories.ls -l– Long listing format.ls -a– Show hidden files.ls -lah– Long listing with human-readable sizes.ls --ignore=test– Ignore files matching a pattern.
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File Creation:
touch– Create an empty file.touch file{1,2,3,4}.txt– Create multiple files.
2. File and Directory Management
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Directories:
mkdir my-new-folder– Create a new directory.mkdir -p ~/temp/subdir– Create nested directories.
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File Operations:
cp s-file d-file– Copy a file.cp -r– Copy directories recursively.mv– Move or rename files or directories.rm– Remove files.rm -r– Remove directories recursively.rm -rf– Force remove files and directories.
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Archives and Compression:
tar -cf archive.tar folder– Create a tar archive.tar -zcf archive.tar.gz folder– Create a compressed tar.gz archive.tar -xzf archive.tar.gz– Extract a tar.gz archive.
3. Searching and Filtering
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Find Files:
find . -name "*.txt"– Find all .txt files in the current directory.find /path -type f -name "*.log"– Search for log files in a directory.find . -type f -exec chmod 644 {} \;– Change permissions of all files.find . -mtime -7– Find files modified in the last 7 days.find . -size +1M– Find files larger than 1MB.find . -empty– Find empty files and directories.
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Grep:
grep "error" file.txt– Search for a pattern in a file.grep -r "error" /var/log– Search recursively in directories.grep -i "error" file.txt– Case-insensitive search.grep -v "pattern" file.txt– Exclude lines with a specific pattern.
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Locate:
locate file-name– Find a file by name.updatedb– Update the file database for locate.
4. File Permissions and Ownership
chmod u=rw,g=rw,o=rw file.txt– Set specific permissions.chmod 777 file.txt– Give full permissions.chmod +x file.sh– Make a file executable.chown user:group file.txt– Change file ownership.chown -R user:group folder– Change ownership recursively.chmod -R 755 folder– Apply permissions recursively.stat file.txt– Display detailed file permissions and metadata.
5. Processes and Job Control
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Process Management:
ps– View running processes.ps aux– Detailed list of processes.ps aux | grep "process-name"– Search for a process.kill -9 PID– Force kill a process.kill -l– List all signal types.
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Job Control:
sleep 1000– Start a long process.ctrl+z– Pause a process.jobs– View background jobs.bg 1– Resume a job in the background.fg 1– Resume a job in the foreground.nice -n 10 process– Start a process with a lower priority.renice -n 5 -p PID– Change priority of a running process.
6. Shell Utilities and Shortcuts
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Redirection:
echo "hello" > file.txt– Redirect output to a file.echo "hello" >> file.txt– Append output to a file.2>– Redirect errors./dev/null– Discard output.
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Pipes:
ps aux | grep "process-name"– Combine commands.cat file.txt | sort | uniq– Sort and remove duplicates.
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Shortcuts:
!!– Repeat the last command.sudo !!– Run the last command as superuser.ctrl+r– Search command history.ctrl+a– Go to the start of the line.ctrl+e– Go to the end of the line.ctrl+w– Delete the previous word.ctrl+u– Clear the current line.
7. Environment Variables
printenv– Show environment variables.export VAR=value– Set a temporary variable.- Set environment variables permanently:
- Add them to
~/.bashrcor~/.bash_profile. - Use
vim ~/.bashrcand add:export VAR=value. - Run
source ~/.bashrcto apply changes.
- Add them to
- System-wide variables:
- Edit
/etc/environmentto set system-wide environment variables.
- Edit
8. Networking
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SSH:
ssh-keygen -t rsa– Generate SSH keys.ssh user@host– Connect to a remote machine.chmod 700 ~/.ssh– Secure SSH directory.
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SFTP:
sftp user@host– Open an SFTP session.pwd– Show the current directory on the remote server.lpwd– Show the current local directory.ls– List files on the remote server.lls– List files locally.put file.txt– Upload a file to the remote server.get file.txt– Download a file from the remote server.bye– Exit the SFTP session.
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Testing Connections:
curl http://localhost:8000/– Test HTTP requests.wget http://example.com/file– Download a file.ping example.com– Test network connectivity.traceroute example.com– Trace the route to a host.netstat -tuln– View network connections.nmap -sP 192.168.1.0/24– Scan a network for devices.
9. Package Management
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APT (Ubuntu/Debian):
apt update– Update package lists.apt upgrade– Upgrade installed packages.apt install package– Install a package.apt autoremove– Remove unused packages.
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YUM (CentOS/RedHat):
yum update– Update packages.yum install package– Install a package.yum remove package– Remove a package.
10. Advanced Commands
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Disk Usage:
df -h– Show disk space usage.du -sh folder– Show folder size.du -ah– Show all files and directories with sizes.
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System Monitoring:
htop– Interactive process viewer.top– Real-time system stats.vmstat– Show system performance metrics.iotop– Monitor disk I/O.
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Logs:
tail -f /var/log/syslog– Monitor logs in real-time.grep "error" /var/log/syslog– Search for errors in logs.
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Advanced File Operations:
rsync -av source/ destination/– Sync files and directories.scp file.txt user@host:/path– Securely copy files to a remote server.dd if=/dev/sda of=/dev/sdb bs=64K conv=noerror,sync– Clone a disk.
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Disk and Partition Management:
fdisk -l– List all disks and partitions.mount /dev/sdX /mnt– Mount a disk.umount /mnt– Unmount a disk.lsblk– List information about block devices.blkid– Get UUID and filesystem information for devices.
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Debugging and Testing:
strace program– Trace system calls.lsof -i :80– List processes using port 80.dmesg– View kernel messages.
11. Automation and Scheduling
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Cron Jobs:
crontab -e– Edit cron jobs for a user.@reboot– Run a task at system startup.0 2 * * *– Schedule a task (e.g., daily at 2 AM).
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At Command:
at 2pm– Schedule a one-time task.atq– View pending tasks.atrm <job_id>– Remove a pending task.
12. Backup and Recovery
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File Backup:
cp -r source_dir backup_dir– Basic directory backup.rsync -av --progress /source /backup– Efficient file synchronization for backup.tar -czvf backup.tar.gz /path/to/directory– Create a compressed backup archive.tar -xzvf backup.tar.gz -C /restore/path– Restore files from a backup archive.
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Database Backup:
mysqldump -u root -p database_name > backup.sql– Backup a MySQL database.mysqldump -u root -p --all-databases > all_backup.sql– Backup all MySQL databases.pg_dump -U username -d database_name -f backup.sql– Backup a PostgreSQL database.
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Database Restoration:
mysql -u root -p database_name < backup.sql– Restore a MySQL database.psql -U username -d database_name -f backup.sql– Restore a PostgreSQL database.
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Snapshot Backups:
rsnapshot config_file– Use rsnapshot for incremental backups.btrfs subvolume snapshot /source /backup/snapshot_name– Create a Btrfs snapshot.
13. Other Useful Commands
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Disk Cleanup:
sudo apt-get clean– Clear cached package files.sudo apt-get autoclean– Remove old cached files.sudo apt-get autoremove– Remove unused packages.
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User Management:
adduser username– Add a new user.passwd username– Set or change a user’s password.deluser username– Delete a user.usermod -aG groupname username– Add a user to a group.
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Networking Tools:
ip a– Display network interfaces and IP addresses.hostnamectl– Manage hostname settings.ifconfig– Display or configure network interfaces (deprecated, useipinstead).
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System Performance:
uptime– Show system uptime and load.free -h– Display memory usage.sar– Monitor CPU usage over time.
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Filesystem Checks:
fsck /dev/sdX– Check and repair a filesystem.tune2fs -l /dev/sdX– Show filesystem parameters.
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Hardware Information:
lscpu– Display CPU architecture details.lsusb– List USB devices.lspci– List PCI devices.