Command Index
Every command used across this folder, in one alphabetical list, with a one-line reminder of what it does and the topic that covers it. Use it to jump from a half-remembered name to the page that explains the flags.
A to C
| Command | Does | Topic |
apt | Install, remove and update packages (Ubuntu) | dpkg and apt |
at | Run a command once at a set time | Cron and at |
auditctl, ausearch | Configure and search the audit log | auditd |
awk | Field-based text processing and sums | awk |
blkid | Show filesystem UUIDs and types | Disks and Devices |
cat, less, head, tail | View file contents | Viewing and Comparing |
chage | Show and set password aging | Passwords and Aging |
chattr, lsattr | Set and read file attributes (+i, +a) | File Attributes |
chcon, restorecon | Change and reset SELinux contexts | SELinux |
chmod, chown, chgrp | Change mode, owner and group | Basic Permissions |
chronyc, timedatectl | Time sync and timezone | Time and Timezones |
chroot | Run with a different root directory | Overlayfs and chroot |
cp, mv, rm | Copy, move and remove files | File Operations |
cron, crontab | Schedule recurring jobs | Cron and at |
curl, wget | Fetch over HTTP and test endpoints | Connectivity Testing |
cut, sort, uniq, tr | Column, sort and character transforms | cut sort uniq tr |
D to G
| Command | Does | Topic |
dd | Block-level copy and image writing | File Operations |
df, du | Filesystem space and directory size | Disk Usage |
dig, host, resolvectl | DNS lookups | DNS Resolution |
dmesg | Kernel ring buffer messages | dmesg and Kernel Messages |
dnf | Install, remove and update packages (RHEL) | rpm and dnf |
dpkg | Low-level package queries (Ubuntu) | dpkg and apt |
dracut | Rebuild the initramfs | Kernel Updates |
find | Search the filesystem by many criteria | Finding Files |
findmnt | Show and verify mounts | Mounting and fstab |
firewall-cmd | Manage firewalld zones and rules | Firewalld and UFW |
free | Memory use, judged by available | Memory |
fuser, lsof | Which process holds a file or mount | Disk Usage |
getcap, setcap | Read and set file capabilities | Capabilities |
getenforce, setenforce, semanage | SELinux mode and policy | SELinux |
getent | Query nsswitch databases | Centralized Identity |
getfacl, setfacl | Read and set ACLs | ACL |
gpg | Sign, verify and encrypt | GPG |
grep | Search text with regular expressions | grep and regex |
groupadd, gpasswd | Create and manage groups | Groups |
grub2-mkconfig, update-grub | Regenerate the GRUB config | GRUB2 |
H to N
| Command | Does | Topic |
hostnamectl | Show and set the hostname | Network Configuration |
id, groups | Show a user's IDs and groups | Groups |
ip | Addresses, links, routes and neighbours | Interfaces and Addresses |
iostat, iotop | Per-disk I/O statistics | Disk I/O |
iscsiadm, targetcli | iSCSI initiator and target | iSCSI and NBD |
journalctl | Query the systemd journal | journalctl |
kill, pkill, killall | Send signals to processes | Signals |
ln | Create hard and symbolic links | Inodes and Links |
logrotate | Rotate and compress logs | logrotate |
losetup | Attach a file as a loop device | Storage and LVM Lab |
lsblk | Tree of block devices | Disks and Devices |
lscpu, lsmem, lshw, lspci | Hardware inventory | System Information |
lsns, unshare, nsenter | Inspect and enter namespaces | Namespaces |
lvcreate, lvextend, pvs, vgs | Manage LVM | LVM |
mdadm | Software RAID arrays | RAID and Encryption |
mkfs, fsck, tune2fs | Create, check and tune filesystems | Filesystems |
modprobe, lsmod, modinfo | Kernel modules | Kernel Modules |
mount, umount | Attach and detach filesystems | Mounting and fstab |
nft, iptables | Packet filtering and NAT | nftables and iptables |
nice, renice, ionice, chrt | Process priority | Priority and Nice |
nmcli, nmtui | NetworkManager configuration (RHEL) | Network Configuration |
O to S
| Command | Does | Topic |
openssl | Inspect certificates, keys and TLS | OpenSSL and Trust Store |
parted, fdisk, gdisk | Partition disks | Partitioning |
podman, skopeo | Run and manage containers | Podman and Quadlet |
ps, pstree, top, htop | View processes | Viewing Processes |
rpm | Low-level package queries (RHEL) | rpm and dnf |
rsync | Efficient copy and mirror | File Transfer |
sar | Historical performance data | Methodology |
scp, sftp | Copy files over SSH | File Transfer |
sed | Stream edit and in-place replace | sed |
ss, netstat | Sockets and listening ports | Ports and Sockets |
ssh, ssh-keygen, ssh-copy-id | Remote login and keys | SSH Client |
strace, ltrace | Trace system and library calls | System Calls and Tracing |
su, sudo, visudo | Switch user and grant privilege | Sudo and su |
swapon, mkswap | Enable and create swap | Swap |
sysctl | Read and set kernel parameters | sysctl |
systemctl | Control services and targets | systemctl |
systemd-analyze, systemd-cgls | Inspect boot and cgroups | systemd Toolbox |
T to Z
| Command | Does | Topic |
tar, gzip, xz, zstd | Archive and compress | Archiving and Compression |
tcpdump | Capture packets | Packet Capture |
tee | Write to a file and stdout | xargs and tee |
timedatectl | Time and timezone | Time and Timezones |
tuned-adm | Apply a performance profile | Tuning |
type, which, command -v | Resolve a command name | Command Resolution |
ulimit | Per-shell resource limits | Limits and File Descriptors |
umask | Default permission mask | umask |
useradd, usermod, userdel | Manage user accounts | Users |
vmstat, mpstat, pidstat | CPU, memory and per-process stats | CPU and Load |
who, w, last | Login sessions and history | Login Sessions |
xargs | Build command lines from input | xargs and tee |