Archive
tar - An archiving utility
zip - Package and compress (archive) files
gzip - Compress to gzip
gunzip - Uncompress gzip
zcat - Uncompress gzip to stdout
bzip2 - A block-sorting file compressor
bunzip2 - Uncompress bzip2
bzcat - Uncompress bzip2 files to stdout
xz - Compress to xz files
unxz - Uncompress xz files
xzcat - Uncompress xz to stdout
lzma - Compress lzma files
unlzma - Uncompress lzma files
lzcat - Uncompress lzma to stdout
cpio - Format of cpio archive files

Module
lsmod - Show the status of modules in the linux kernel
modinfo - Show information about a linux kernel module
insmod - Simple program to insert a module into the linux kernel
modprobe - Add and remove modules from the linux kernel (more clever than insmod, can handle dependencies)
rmmod - Simple program to remove a module from the linux kernel

Other
mail - Send and receive Internet mail
watch - Execute a program periodically, showing output fullscreen
sleep - Delay for a specified amount of time
xargs - Build and execute command lines from standard input
iostat - Report central processing unit (cpu) statistics and input/output statistics for devices and partitions.
dd - Convert and copy a file
xhost - Server access control program for x

Package
rpm - Centos package installer
rpm2cpio - Extract cpio archive from rpm package manager (rpm) package.
yum - Centos package manager
dnf - Fedora packege manager (advanced features then yum)
dpkg - Debian package installer
apt - Debian package manager

Permission
chown - Change file owner and group
chgrp - Change group ownership
chmod - Change file mode bits
umask - Display or set file mode mask.

Process
ps - Report a snapshot of the current processes.
top - Display linux processes
kill - Terminate a process
nohup - Run a command immune to hangups, with output to a non-tty
nice - Run a program with modified scheduling priority
renice - Alter priority of running processes
pgrep - Look up on processes based on name and other attributes
pkill - Signal processes based on name and other attributes

RAID
mdadm - Manage md devices aka linux software raid

Shell
cd - Change working directory
pwd - Print name of current/working directory
history - Manipulate the history list
type - Display information about command type, determin if external or buiilt-in shell command
alias - Display or define aliases
unalias - Remove aliases

System
uname - Print system information
uptime - Tell how long the system has been running
w - Show who is logged on and what they are doing
who - Show who is logged on
free - Display amount of free and used memory in the system
df - Report file system disk space usage
du - Estimate file space usage
blkid - Locate/print block device attributes
locale - Perl pragma to use or avoid posix locales for built-in operations
hwclock - Time clocks utility, bios
date - Print or set the linux system date and time
upower - Upower command line tool
halt - Stops processes and CPU
shutdown - Stops processes, CPU and send poweroff signal to the hardware
poweroff - Stops processes, CPU and send poweroff signal to the hardware
reboot - Reboot the machine
swapon - Enable devices and files for paging and swapping
swapoff - Disable devices and files for paging and swapping
mount - Mount a filesystem or display monted filesystems

Systemd
systemctl - Control the systemd system and service manager
journalctl - Query the systemd journal
timedatectl - Control the system time and date
localectl - Control the system locale and keyboard layout settings

Terminal
screen - Screen manager with vt100/ansi terminal emulation
tmux - Terminal multiplexer

Text
echo - Display a line of text
cat - Concatenate files and print on the standard output
tac - Concatenate and print files in reverse
paste - Merge lines of files
split - Split a file into pieces
sort - Sort lines of text files
uniq - Report or omit repeated lines
nl - Number lines of files
more - File perusal filter for crt viewing
less - Opposite of more
head - Output the first part of files
tail - Output the last part of files
wc - Print newline, word, and byte counts for each file
cut - Remove sections from each line of files
grep - Print lines that match patterns, basic regular expresion
egrep - Print lines that match patterns, extended regular expresion
fgrep - Fixed strings, not regular expressions
tr - Translate or delete characters
awk - gawk is a pattern scanning and processing language

Message
wall - Write a message to all users
notify-send - A program to send desktop notifications
mesg - Display (or do not display) messages from other users

Manual
man - An interface to the system reference manuals
apropos - Search the manual page names and descriptions
whatis - Display one-line manual page descriptions
mandb - Create or update the manual page index caches

Binary
od - Dump files in octal and other formats
xxd - Make a hexdump or do the reverse

Checksum
md5sum - Compute and check md5 message digest
sha1sum - Compute and check SHA1 message digest
sha256sum - Compute and check SHA256 message digest
sha512sum - Compute and check SHA512 message digest

Editor
vim - Vi improved, a programmer's text editor
vimtutor - The vim tutor
nano - Nano's ANOther editor, an enhanced free Pico clone
sed - Stream editor for filtering and transforming text

File
ls - List directory contents
touch - Change file timestamps
file - Determine file type
mkdir - Make directories
cp - Copy files and directories
mv - Move (rename) files
rm - Remove files or directories

File System
fdisk - Manipulate disk partition table
parted - A partition manipulation program
gdisk - Interactive guid partition table (gpt) manipulator
mkfs.ext4 - Create an ext4 filesystem
mkfs.vfat - Create an FAT filesystem
mkfs.xfs - Create an XFS filesystem
mkswap - Set up a linux swap area
chattr - Change file attributes on a linux file system
debugfs - Ext2/ext3/ext4 file system debugger
dumpe2fs - Dump ext2/ext3/ext4 filesystem information
e2label - Change the label on an ext2/ext3/ext4 filesystem
resize2fs - Ext2/ext3/ext4 file system resizer
tune2fs - Adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems
xfs_admin - Change parameters of an xfs filesystem
xfs_db - Debug an xfs filesystem
xfs_fsr - Filesystem reorganizer for xfs
xfs_info - Display xfs filesystem geometry information
xfs_repair - Repair an xfs filesystem
fsck - Check and repair a linux filesystem

Find
find - Search for files in a directory hierarchy
whereis - Locate the binary, source, and manual page files for a command
which - Shows the full path of (shell) commands.
locate - Find files by name from database
updatedb - Update a database for mlocate

Hardware
lsdev - Display information about installed hardware
lsblk - List block devices
lspci - List all pci devices
lsusb - List usb devices
lscpu - Display information about the CPU architecture
setpci - Configure pci devices (change ioports)

Job
jobs - Display status of jobs
fg - Move job to the foreground.
bg - Move jobs to the background.

Library
ldd - Print shared object dependencies
ldconfig - Configure dynamic linker run-time bindings

Link
readlink - Print resolved symbolic links or canonical file names
ln - Make links between files
unlink - Call the unlink function to remove the specified file

LVM
pvcreate - Initialize physical volume(s) for use by lvm
vgcreate - Create a volume group
lvcreate - Create a logical volume

User
useradd - Create a new user or update default new user information
userdel - Delete a user account and related files
usermod - Modify a user account
groupadd - Create a new group
groups - Display current group names
newgrp - Log in to a new group
passwd - Change password
chage - Change user password expiry information
getent - Get entries from administrative database.

Linux Commands