Linux Cheat Sheet¶

Scannable commands for the Linux for Cloud & DevOps track. Prefer full tutorials when you need why, not only how.

Commands¶

Task	Commands
Identity	`uname -a`; `hostnamectl`; `cat /etc/os-release`; `uptime`
Navigate	`pwd`; `ls -la`; `cd`; `cd -`; `tree -L 2`
Files	`cp -a`; `mv`; `rm -i`; `mkdir -p`; `touch`; `stat`; `file`
View	`cat`; `less`; `head -n`; `tail -f`; `wc -l`
Find	`find /path -name '*.log'`; `find /path -mtime -1`; `locate` (if indexed)
Archive	`tar -czf a.tgz dir`; `tar -xzf a.tgz`; `gzip -d`
Help	`man cmd`; `cmd --help`; `type cmd`; `command -v cmd`

Task	Commands / notes
Modes	`chmod 640 file`; `chmod u+x script`; `umask`
Ownership	`chown user:group file`; `chgrp group file`
Special bits	Sticky `chmod 1777 /tmp`-style; SUID/SGID on binaries/dirs (`chmod u+s` / `g+s` / `2770`)
Inspect	`ls -l`; `namei -l /path`; `id`; `groups`
ACLs	`getfacl path`; `setfacl -m u:alice:rwx path`; `setfacl -b path`
sudo	`sudo -l`; `sudo -u user cmd`; files under `/etc/sudoers.d` (`visudo -cf`)

Tool	Pattern
grep	`grep -RIn 'ERROR' /var/log`; `grep -E 'pattern'`; `-v` invert
sed	`sed -n '1,20p'`; `sed 's/foo/bar/g'`
awk	`awk '{print $1}'`; `awk -F: '{print $1}' /etc/passwd`
cut/tr	`cut -d: -f1`; `tr '[:upper:]' '[:lower:]'`
sort/uniq	`sort \\| uniq -c \\| sort -nr`
xargs	`find . -name '*.tmp' -print0 \\| xargs -0 rm -f`

Task	Commands
List	`ps aux`; `ps -ef`; `pgrep -a name`
Interactive	`top`; `htop`
Signals	`kill -TERM <pid>`; `kill -KILL <pid>`; `pkill -f pattern`
Priority	`nice -n 10 cmd`; `renice -n 5 -p <pid>`
Jobs	`jobs`; `bg`; `fg`; `nohup cmd &`; `disown`
Limits	`ulimit -a`; systemd `MemoryMax=` / `CPUQuota=`

Task	Commands
Inventory	`lsblk -f`; `blkid`; `findmnt`
Usage	`df -hT`; `df -i`; `du -sh *`; `du -x -d1 /`
Filesystems	`mkfs.ext4`; `mkfs.xfs`; `mount`; `umount`
Persist	UUID in `/etc/fstab`; `findmnt --verify`
LVM	`pvs`; `vgs`; `lvs`; `lvextend`; `resize2fs` / `xfs_growfs`
Swap	`swapon --show`; `free -h`

Task	Commands
Addresses	`ip -br a`; `ip route`; `ip neigh`
Sockets	`ss -tulpn`; `ss -tp`
Path	`ping -c 3 host`; `traceroute host`; `tracepath`
DNS	`dig +short name`; `resolvectl query name`; `getent hosts`
HTTP	`curl -vI https://example`; `wget`
Capture	`tcpdump -i any port 443`; `nc` / `ncat`

Task	Commands / settings
Keys	`ssh-keygen -t ed25519`; `ssh-copy-id -i key.pub user@host`
Connect	`ssh -i key user@host`; `scp`; `sftp`
Config	`~/.ssh/config` `Host` stanzas; `IdentitiesOnly yes`
Server	`sshd -t`; `sshd -T`; drop-ins in `/etc/ssh/sshd_config.d/`
Hardening	`PasswordAuthentication no`; `PermitRootLogin no`; keep console/out-of-band

Task	Commands
Units	`systemctl status name`; `start`/`stop`/`restart`/`reload`
Boot	`systemctl enable --now name`; `is-enabled`; `list-unit-files`
Failures	`systemctl --failed`; `systemctl reset-failed`
Journal	`journalctl -u name -f`; `--since today`; `-p err`; `-o short-iso`
Timers	`systemctl list-timers`; `systemctl status name.timer`
Analyse	`systemd-analyze blame`; `systemd-analyze critical-chain`

Family	Update / install / query
Debian/Ubuntu	`apt update`; `apt install pkg`; `apt remove`; `dpkg -l`; `apt-cache policy`
RHEL/Fedora	`dnf install pkg`; `dnf upgrade`; `rpm -qa`; `dnf info`
SUSE	`zypper refresh`; `zypper install`
Universal	`snap`; `flatpak` (use sparingly on servers; prefer distro packages)

Symptom	First commands
Service down	`systemctl status`; `journalctl -u` `--since`
High CPU	`uptime`; `ps --sort=-pcpu`; `top`; `vmstat 1`
Memory pressure	`free -h`; `ps --sort=-pmem`; check OOM in `journalctl -k`
Disk full	`df -h`; `df -i`; `du -x -d1`; clear safe logs/caches
Network	`ip r`; `ss -tulpn`; `ping`; `dig`; cloud SG/NSG
Slow disk	`iostat -xz 1`; `dmesg -T \\| tail`
Permissions	`namei -l`; `id`; `getfacl`; compare to expected owner/mode
Boot	`journalctl -b`; `systemd-analyze`; rescue/single-user carefully