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Linux
Essential Linux commands for file management, permissions, processes, networking, disk usage, users, and system administration
File & Directory Operations
Navigation, listing, creating, copying, moving, and finding files
bash·Navigate & list
# Navigate cd /path/to/dir # change directory cd ~ # go home cd - # go to previous directory pwd # print working directory # List ls -la # long format, including hidden ls -lh # human-readable sizes ls -lt # sort by modification time ls -R # recursive listing
bash·Create / copy / move / delete
mkdir -p a/b/c # create nested dirs touch file.txt # create empty file / update timestamp cp -r src/ dest/ # copy directory recursively mv old.txt new.txt # move / rename rm -rf dir/ # remove directory and contents (careful!) ln -s /path/to/orig link # create symlink
bash·Find files
find . -name "*.log" -mtime -7 # modified in last 7 days
find . -type f -size +100M # files larger than 100 MB
find . -name "*.sh" -exec chmod +x {} \; # exec on each match
locate filename # fast index-based search (needs updatedb)
which python3 # location of a binary
type bash # type info (alias/builtin/file)File Content & Text Processing
cat, less, head, tail, grep, awk, sed, sort, cut and other text tools
bash·View content
cat file.txt # print entire file less file.txt # paginated view (q to quit) head -n 20 file.txt # first 20 lines tail -n 50 file.txt # last 50 lines tail -f /var/log/syslog # follow live output
bash·Search with grep
grep -r "pattern" /path/ # recursive search grep -i "error" app.log # case-insensitive grep -n "TODO" *.ts # show line numbers grep -v "debug" app.log # invert match (exclude) grep -E "err|warn" app.log # extended regex (OR) grep -l "pattern" *.txt # only filenames
bash·Transform & process
sort file.txt # sort lines
sort -u file.txt # sort and deduplicate
uniq -c sorted.txt # count consecutive dupes
cut -d',' -f1,3 data.csv # extract columns 1 and 3
awk '{print $1, $3}' file.txt # print fields 1 and 3
awk -F':' '{print $1}' /etc/passwd # custom delimiter
sed 's/foo/bar/g' file.txt # replace all occurrences
sed -i 's/old/new/g' file.txt # in-place edit
wc -l file.txt # count lines
diff a.txt b.txt # show differencesPermissions & Ownership
chmod, chown, setuid/setgid/sticky bits, ACLs, and umask
bash·chmod — change mode
# Permission notation: rwxrwxrwx (owner/group/other) # r=4, w=2, x=1 chmod 755 script.sh # rwxr-xr-x chmod 644 file.txt # rw-r--r-- chmod +x script.sh # add execute bit for all chmod -R 750 /app/ # recursive # Special bits chmod u+s binary # setuid — run as file owner chmod g+s /shared/ # setgid — new files inherit group chmod +t /tmp/ # sticky bit — only owner can delete
bash·chown & ACLs
# chown — change owner chown user:group file.txt chown -R www-data:www-data /var/www/ # View permissions ls -la stat file.txt # detailed metadata # ACLs (extended permissions) getfacl file.txt setfacl -m u:alice:rw file.txt setfacl -x u:alice file.txt # remove ACL entry # umask — default permission mask umask # show current mask (e.g. 022) umask 027 # new files: 640, dirs: 750
Process Management
ps, kill, background jobs, nice/renice, lsof, and strace
bash·View & kill processes
ps aux # all processes, detailed ps aux | grep nginx top # live process viewer htop # interactive (install separately) pgrep nginx # find PID by name pidof nginx # Signals kill PID # SIGTERM (graceful) kill -9 PID # SIGKILL (force) killall nginx # kill by name pkill -f "python app.py" # kill by command pattern
bash·Background jobs & priority
command & # run in background jobs # list background jobs fg %1 # bring job 1 to foreground bg %1 # resume job 1 in background nohup command & # immune to hangup disown %1 # detach job from shell # nice / renice — priority (-20 high → 19 low) nice -n 10 command # start with lower priority renice -n 5 -p PID # adjust running process # Monitoring lsof -i :8080 # processes using port 8080 lsof -p PID # files opened by PID strace -p PID # trace system calls watch -n 2 'ps aux | grep app' # repeat every 2s
Disk & Storage
df, du, lsblk, mount/umount, fdisk, LVM, and filesystem tools
bash·Disk usage
df -h # filesystem usage (human-readable) df -h / # specific filesystem du -sh /var/log/ # total size of directory du -sh * | sort -h # sizes of all items, sorted du -ah --max-depth=1 / # one level deep
bash·Block devices & mounts
lsblk # list block devices (tree) blkid # show UUIDs and FSTypes fdisk -l # partition table (requires root) mount # list mounted filesystems mount /dev/sdb1 /mnt/data # mount device umount /mnt/data # unmount # Persistent mounts — /etc/fstab # UUID=xxxx /mnt/data ext4 defaults 0 2 # Filesystem tools mkfs.ext4 /dev/sdb1 # format as ext4 fsck /dev/sdb1 # check and repair (unmounted) resize2fs /dev/vg0/lv_data # grow filesystem after LV extend
bash·LVM
pvs / vgs / lvs # show PVs, VGs, LVs lvcreate -L 10G -n lv_data vg0 # create logical volume lvextend -L +5G /dev/vg0/lv_data # extend LV resize2fs /dev/vg0/lv_data # grow ext4 filesystem lvremove /dev/vg0/lv_data # remove LV
Networking
ip, ping, dig, ss/netstat, curl, scp, rsync, and ufw
bash·Interfaces, routing & DNS
ip addr show # all interfaces and IPs ip addr show eth0 # specific interface ip link set eth0 up/down # enable/disable interface ip route show # routing table ip route add default via 192.168.1.1 ping -c 4 8.8.8.8 # ICMP ping traceroute 8.8.8.8 # path tracing dig example.com # DNS lookup dig example.com +short # just the IP nslookup example.com
bash·Open ports & connections
ss -tlnp # TCP listening ports with PID ss -an | grep :80 # connections on port 80 netstat -tlnp # older alternative to ss lsof -i :443 # processes on port 443
bash·Transfer & sync
curl -O https://example.com/file.tar.gz # download
curl -I https://example.com # headers only
curl -d '{"key":"val"}' -H 'Content-Type: application/json' https://api.example.com
wget https://example.com/file.zip
scp user@host:/path/file . # secure copy from remote
rsync -avz --progress src/ user@host:/dest/ # sync filesbash·Firewall (ufw)
ufw status ufw allow 22/tcp ufw allow from 10.0.0.0/8 to any port 5432 ufw deny 3306 ufw delete allow 3306 ufw enable ufw disable
Users & Groups
whoami, id, useradd/usermod/userdel, groups, sudo, and su
bash·Current user & context
whoami # current username id # uid, gid, groups groups # groups current user belongs to who # logged-in users w # logged-in users + activity last # login history
bash·User management
useradd -m -s /bin/bash alice # create with home dir useradd -m -G sudo,docker alice # add to groups at creation usermod -aG docker alice # add to group usermod -s /bin/zsh alice # change shell userdel -r alice # delete user and home dir passwd alice # set/change password chage -l alice # password expiry info chage -E 2026-12-31 alice # set account expiry
bash·Groups & sudo
groupadd devs groupdel devs gpasswd -a alice devs # add user to group gpasswd -d alice devs # remove user from group sudo command # run as root sudo -u postgres psql # run as specific user sudo -i # interactive root shell visudo # safely edit /etc/sudoers su - alice # switch to alice (login shell) su - # switch to root
System Info & Logs
uname, lscpu, free, systemctl, journalctl, and system logs
bash·OS & hardware info
uname -a # kernel version and arch hostnamectl # hostname, OS, kernel info cat /etc/os-release # distro information lscpu # CPU details free -h # memory usage lspci # PCI devices lsusb # USB devices uptime # uptime and load averages last reboot # reboot history
bash·Systemd services
systemctl status nginx systemctl start / stop / restart / reload nginx systemctl enable / disable nginx # start at boot systemctl list-units --type=service --state=running journalctl -u nginx -f # follow service logs journalctl -u nginx --since "1 hour ago" journalctl -xe # recent errors
bash·Logs & time
tail -f /var/log/syslog tail -f /var/log/auth.log # auth/sudo events grep -i error /var/log/messages timedatectl # current time/timezone timedatectl set-timezone America/New_York date # current date/time hwclock # hardware clock
Shell Productivity & Scripting
History tricks, redirection, pipes, variables, loops, and useful aliases
bash·History & shortcuts
history | grep ssh # search command history !! # repeat last command !ssh # repeat last ssh command Ctrl+R # reverse history search Ctrl+C # kill foreground job Ctrl+Z # suspend foreground job Ctrl+D # send EOF / exit shell
bash·Redirection & pipes
command > file.txt # stdout to file (overwrite) command >> file.txt # stdout to file (append) command 2> err.txt # stderr to file command &> all.txt # stdout+stderr to file command 2>&1 | tee out.txt # both to pipe and file command1 | command2 # pipe stdout to next command
bash·Variables, conditionals & loops
export VAR="value"
echo "Hello, $VAR"
VAR=$(command) # capture command output
# Conditionals
if [ -f /etc/hosts ]; then echo "exists"; fi
[ -d /tmp ] && echo "dir exists"
[ -z "$VAR" ] && echo "empty"
# Loops
for f in *.log; do gzip "$f"; done
while read line; do echo "$line"; done < file.txt
# Useful aliases & tricks
alias ll='ls -lahF'
xargs -P4 -I{} command {} # parallel execution
seq 1 10 | xargs -I{} echo "item {}"
env # all environment variables
export PATH="$PATH:/usr/local/bin"Archives & Package Management
tar, zip, apt, dnf/yum, dpkg/rpm, snap and flatpak
bash·tar & zip
# tar tar -czf archive.tar.gz dir/ # create gzip archive tar -cjf archive.tar.bz2 dir/ # create bzip2 archive tar -xzf archive.tar.gz # extract gzip tar -xzf archive.tar.gz -C /dest/ # extract to directory tar -tzf archive.tar.gz # list contents tar -czf - dir/ | ssh user@host 'tar -xzf - -C /dest/' # zip / unzip zip -r archive.zip dir/ zip -r -e secure.zip dir/ # with password unzip archive.zip unzip -l archive.zip # list contents unzip archive.zip -d /dest/
bash·apt (Debian/Ubuntu)
apt update # refresh package index apt upgrade # upgrade all packages apt install nginx apt remove nginx apt autoremove # remove unused dependencies apt search keyword apt show nginx dpkg -l | grep nginx # list installed matching
bash·dnf/yum (RHEL/CentOS/Fedora)
dnf update dnf install nginx dnf remove nginx dnf search keyword rpm -qa | grep nginx # list installed RPMs rpm -qi nginx # package info rpm -ql nginx # list package files # Snap / Flatpak snap install code --classic flatpak install flathub com.spotify.Client