LINUX ESSENTIALS CHEATSHEET
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1. SYSTEM & HARDWARE
uname -a                 Kernel and architecture info
lsb_release -a           Distribution version
uptime                   System uptime and load average
free -h                  RAM and swap usage
df -h                    Disk space usage by mountpoint
du -sh *                 Size of folders in current directory

2. PROCESSES & LOGS
top / htop               Interactive process viewer
ps aux | grep <name>     Find running process
kill -15 <pid>           Graceful stop (SIGTERM)
journalctl -xe           Recent system errors
journalctl -u <svc> -f   Follow logs of a systemd service

3. FILES & PERMISSIONS
chmod 644 file           rw-r--r-- (standard file)
chmod 755 script.sh      rwxr-xr-x (executable / directory)
chown user:group file    Change owner and group
tar -czf out.tar.gz dir  Create compressed archive
tar -xzf out.tar.gz      Extract compressed archive
find /var/log -name "*.log" -mtime +7   Find logs older than 7 days