Linux Admin Cheatsheets

Schnelle Command-Referenzen für den täglichen Admin-Einsatz.

sudo useradd -m -s /bin/bash user
sudo userdel -r user
sudo passwd user
sudo usermod -aG sudo user

chmod 755 file.sh
chown user:group file
chmod -R 644 /var/www

sudo systemctl start|stop|restart service
sudo systemctl enable|disable service
journalctl -u service -f

sudo apt update && sudo apt upgrade
sudo apt install package
sudo apt remove package
apt search keyword

sudo dnf check-update
sudo dnf install package
sudo dnf remove package

sudo ufw allow 80/tcp
sudo ufw deny 23/tcp
sudo ufw enable
sudo ufw status

ssh-keygen -t ed25519
ssh-copy-id user@host
ssh -p 2222 user@host

ip addr show
ip route show
ss -tulpn
netstat -tulpn

nslookup domain.com
dig domain.com
host domain.com

find /path -name "*.log"
grep -r "pattern" /path
tail -f /var/log/syslog

df -h
du -sh /path
ncdu /path

tar -czf backup.tar.gz /path
tar -xzf backup.tar.gz

rsync -avz /source/ /dest/
rsync -avz -e ssh /local user@host:/remote

Weitere hilfreiche Resources:

• Vim Cheatsheet
• tmux Cheatsheet
• Regex Cheatsheet

System Administration

User Management

# User anlegen/löschen
sudo useradd -m -s /bin/bash username
sudo userdel -r username
sudo passwd username

# Gruppen
sudo groupadd groupname
sudo usermod -aG sudo username
groups username

# Su sudo
sudo su - username
sudo -u username command

Permissions

# Chmod
chmod 755 file.sh
chmod u+x file.sh
chmod -R 644 /var/www

# Chown
chown user:group file
chown -R www-data:www-data /var/www

# Umask
umask 022

Systemd

sudo systemctl start|stop|restart|reload service
sudo systemctl enable|disable service
sudo systemctl status service
systemctl list-units --type=service
journalctl -u service -f

Package Management

# APT (Debian/Ubuntu)
sudo apt update && sudo apt upgrade
sudo apt install package
sudo apt remove package
apt search keyword

# DNF (RHEL/CentOS)
sudo dnf check-update
sudo dnf install package
sudo dnf remove package
dnf search keyword

# Zypper (openSUSE)
sudo zypper refresh
sudo zypper install package

Networking

# IP Configuration
ip addr show
ip link set eth0 up|down
ip route show

# DNS
nslookup domain
dig domain
host domain

# Connectivity
ping -c 4 host
traceroute host
netstat -tulpn
ss -tulpn

# Firewall (ufw)
sudo ufw allow 80/tcp
sudo ufw enable
sudo ufw status

File Operations

# Find Files
find /path -name "*.log"
find /path -mtime -7
find /path -size +100M

# Disk Usage
df -h
du -sh /path
du -h --max-depth=1

# Archive
tar -czf archive.tar.gz /path
tar -xzf archive.tar.gz
zip -r archive.zip /path

Process Management

# Processes
ps aux | grep process
top
htop
kill PID
killall processname
pkill pattern

# Background Jobs
command &
jobs
fg %1
bg %1
nohup command &

Text Processing

# Grep
grep -r "pattern" /path
grep -v "pattern" file
grep -i "pattern" file

# Sed
sed 's/old/new/g' file
sed -i 's/old/new/g' file

# Awk
awk '{print $1}' file
awk -F: '{print $1}' /etc/passwd

# Sort/Uniq
sort file
sort -n file
uniq file
sort file | uniq -c

Monitoring

# System Load
uptime
w
top
htop

# Memory
free -h
vmstat
cat /proc/meminfo

# Disk I/O
iostat
iotop

# Network
iftop
nethogs

SSH

# Connect
ssh user@host
ssh -p 2222 user@host
ssh -i key.pem user@host

# Copy Files
scp file user@host:/path
scp -r dir user@host:/path
rsync -avz /local user@host:/remote

# Tunneling
ssh -L 8080:localhost:80 user@host
ssh -D 1080 user@host

Logs

# View Logs
tail -f /var/log/syslog
journalctl -f
journalctl -u service
journalctl --since "1 hour ago"

# Log Rotation
logrotate -f /etc/logrotate.conf

Backup & Recovery

# Tar Backup
tar -czf backup.tar.gz /etc /home
tar -xzf backup.tar.gz

# Rsync
rsync -avz --delete /source/ /backup/
rsync -avz -e ssh /local user@host:/remote

# DD
dd if=/dev/sda of=/backup/disk.img bs=4M
dd if=/backup/disk.img of=/dev/sda bs=4M

Performance

# CPU Info
lscpu
cat /proc/cpuinfo

# Memory Info
free -h
cat /proc/meminfo

# Disk Performance
hdparm -Tt /dev/sda
dd if=/dev/zero of=testfile bs=1G count=1 oflag=direct

One-Liners

# Top 10 größte Dateien
find . -type f -exec du -h {} + | sort -rh | head -10

# Offene Ports anzeigen
netstat -tulpn | grep LISTEN

# CPU-intensive Prozesse
ps aux | sort -nrk 3,3 | head -5

# Memory-intensive Prozesse
ps aux | sort -nrk 4,4 | head -5

# Anzahl Dateien pro Verzeichnis
find . -maxdepth 1 -type d | while read dir; do echo -n "$dir: "; find "$dir" -type f | wc -l; done

# Failed SSH Logins
grep "Failed password" /var/log/auth.log | awk '{print $11}' | sort | uniq -c | sort -rn

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