README.md

command-center

Commonly available command-line tools for Linux distros listed somewhat categorically.

Help

• man - format and display the on-line manual pages (tldr, die, manned)
• info - read info docs (tldr, die, manned)
• whatis - search the whatis database for complete words (tldr, die, manned)
  • apropos - search the whatis database for string (tldr, die, manned)

Terminal

• printf - format and print data (tldr, manned)
• printenv - print all or part of environment (tldr, die, manned)
• clear - clear the terminal screen (tldr, die, manned)
• tty - print the file name of the terminal connected to standard input (tldr, die, manned)
• stty - change and print terminal line settings (tldr, die, manned)
• setterm - set terminal attributes (manned)
• screen - screen manager with VT100/ANSI terminal emulation (tldr, die, manned)
• cd - Change the current working directory (tldr, manned)
• alias - define or display aliases (tldr, manned)
  • unalias - remove alias definitions (tldr, manned)
• locale - get locale-specific information (tldr, manned)
• tput - initialize a terminal or query terminfo database (tldr, manned)
  • reset - terminal initialization (tldr, manned)
  • tset - terminal initialization (manned)
• getopts - parse utility options (manned)
• read - read from standard input into shell variables (tldr, manned)
• true - do nothing, successfully (tldr, manned)
• false - do nothing, unsuccessfully (tldr, manned)

History

• fc - process the command history list (tldr, manned)
• history - GNU History Library (tldr, manned)

Typescripts

• script - make typescript of terminal session (tldr, manned)
• scriptreplay - play back typescripts, using timing information (tldr, manned)
• scriptlive - re-run session typescripts, using timing information (manned)

Hardware

Hardware Information

• lshw - list hardware information (tldr, die, manned)
• lscpu - list CPU architecture information (tldr, die, manned)
  • cat /proc/cpuinfo
• lspci - list all PCI devices (tldr, die, manned)
• lsusb - list USB device info (tldr, die, manned)
• free - display amount of free and used memory in the system (tldr, die, manned)
• lsmem - list the ranges of available memory with their online status (manned)
• nproc - print the number of processing units available (tldr, manned)

Hardware Configuration

• chcpu - configure CPUs (tldr, die, manned)
• chmem - configure memory (manned)
• eject - eject removable media (tldr, manned)

System

System Information

• uname - print system information (tldr, die, manned)
  • arch - print machine hardware name (same as uname -m) (tldr, manned)
• setarch - change reported architecture in new program environment and/or set personality flags (manned)
• last - show listing of last logged in users / last reboot (tldr, die, manned)
• lslogins - display information about known users in the system
• uptime - tell how long the system has been running (tldr, die, manned)
• runlevel - output previous and current runlevel (die, manned)
• dmesg - print or control the kernel ring buffer (tldr, die, manned)
• logger - enter messages into the system log (tldr, manned)

System State

• login - sign on (tldr, die, manned)
  • newgrp - log in to a new group (tldr, manned)
• sulogin - single-user login (manned)
• reboot - reboot or stop the system (tldr, die, manned)
• shutdown - bring the system down (tldr, die, manned)
• poweroff - reboot or stop the system (tldr, die, manned)
• rtcwake - enter a system sleep state until specified wakeup time (tldr, manned)
• telinit - change system runlevel (die, manned)
• ctrlaltdel - set the function of the Ctrl-Alt-Del combination (tldr, manned)

System Date/Time

• date - print or set the system date and time (tldr, die, manned)
• cal - displays a calendar (tldr, die, manned)
• calendar - reminder service (holidays, meetings, ...) (tldr, die, manned)
• sleep - delay for a specified amount of time (tldr, die, manned)
• hwclock - time clocks utility (tldr, manned)

Namespaces

• nsenter - run program in different namespaces (tldr, manned)
• lsns - list namespaces (tldr, manned)
• unshare - run program in new namespaces (tldr, manned)

Users/Groups

Users

User Information

• logname - print current user's login name (tldr, die, manned)
• id - print real and effective user and group IDs (tldr, die, manned)
  • whoami - print effective userid. same as id -un (tldr, die, manned)
• w - show who is logged on and what they are doing (tldr, die, manned)
• who - show who is logged on (tldr, die, manned)
  • utmpdump - dump UTMP and WTMP files in raw format (tldr, manned)
• users - print the user names of users currently logged in to the current host (tldr, die, manned)
• finger - user information lookup program (tldr, die, manned)
  • pinky - lightweight finger (tldr, manned)

User Management

• useradd - create a new user or update default new user information (tldr, die, manned)
  • newusers - update and create new users in batch (die, manned)
• usermod - modify a user account (tldr, die, manned)
• userdel - delete a user account and related files (tldr, die, manned)
• passwd - update user's authentication (tldr, die, manned)
• chsh - change your (or another user's) login shell (tldr, die, manned)
• chpasswd - update passwords in batch mode (tldr, die, manned)
• vipw - edit the password file (tldr, manned)
• vigr - edit the group file (manned)
• chfn - change your (or another user's) finger information (tldr, die, manned)

User Communication

• wall - write a message to all users (tldr, manned)
• mesg - display (or do not display) messages from other users (tldr, manned)
• write - send a message to another user (tldr, die, manned)

User Substituion/Masquerading

• su - run a shell with substitute user and group IDs (tldr, die, manned)
• runuser - run a shell with substitute user and group IDs (tldr, die, manned)
• setpriv - run a program with different Linux privilege settings (manned)
• sudo - execute a command as another user (tldr, die, manned)
• visudo - edit the sudoers file (tldr, die, manned)
• sudoreplay - replay sudo session logs (die, manned)
  • sudoreplay -l user millert - list sessions ran by user millert
  • sudoreplay -l user bob command vi - list sessions run by user bob with a command containing the string vi

Groups

• groups - print the groups a user is in (tldr, die, manned)
• groupadd - create a new group (tldr, die, manned)
• groupmod - modify a group definition on the system (tldr, die, manned)
• groupdel - delete a group (tldr, die, manned)

Processes/Tasks/Commands

Process Information

• strace -p <pid> -p <pid> ... - trace one or more currently running process IDs (tldr, die, manned)
• ps - report a snapshot of the current processes (tldr, die, manned)
• pgrep - look up processes based on name and other attributes (tldr, die, manned)
  • pgrep -a <pattern> - list complete command line
  • pgrep -f <pattern> - use full process name to match
• top - display Linux tasks (tldr, die, manned)
  • htop - interactive process viewer (tldr, die, manned)
  • iotop - simple top-like I/O monitor (tldr, die, manned)
• pstree - display a tree of processes (tldr, die, manned)
• taskset - retrieve or set a process's CPU affinity (tldr, die, manned)
• fuser - show which processes use the named files, sockets, or filesystems (tldr, die, manned)

Update Process Information

• renice - alter priority of running processes (tldr, die, manned)
• chrt - manipulate real-time attributes of a process (tldr, die, manned)
• choom - display and adjust OOM-killer score (manned)
• prlimit - get and set process resource limits (tldr, manned)

Kill/Signal Process

• kill - terminate a process (tldr, die, manned)
• killall - kill processes by name (tldr, die, manned)
• pkill - signal processes based on name and other attributes (tldr, die, manned)

Run Command

• xargs - build and execute command lines from standard input (tldr, manned)
• time - time a simple command or give resource usage (tldr, die, manned)
• timeout - run a command with a time limit (tldr, die, manned)
• setsid - run a program in a new session (tldr, manned)
• strace - run a command and trace system calls and signals (tldr, die, manned)
• nice - run a command with modified scheduling priority (tldr, die, manned)
• nohup - run a command immune to hangups, with output to a non-tty (tldr, die, manned)
• env - run a command in a modified environment (tldr, die, manned)
• watch - run a command periodically, displaying its output (tldr, die, manned)
• daemonize - run a program as a Unix daemon (tldr, die, manned)

Jobs/Schedule Command

• fg - run jobs in the foreground (tldr, manned)
• bg - run jobs in the background (tldr, manned)
• jobs - display status of jobs in the current session (tldr, manned)
• wait - wait for process to change state (tldr, manned)
• at - executes commands at a specified time (tldr, die, manned)
  • atq - list pending jobs (tldr, die, manned)
  • atrm - remove jobs by ID (tldr, die, manned)
  • batch - executes commands when system load levels permit (tldr, die, manned)
• cron
  • crontab - maintain crontab files for individual users (tldr, die, manned)

Inter-Process Communication

• ipcmk - make various IPC resources (tldr, manned)
• ipcs - show information on IPC facilities (tldr, manned)
• lsipc - show information on IPC facilities currently employed in the system (manned)
• ipcrm - remove certain IPC resources (tldr, manned)

Networking

Network Configuration

• ip - show / manipulate routing, devices, policy routing and tunnels (tldr, die, manned)
  • iptunnel - creates, deletes, and displays configured tunnels (die, manned)
• ifconfig - configure a network interface (tldr, die, manned)
  • replaced by ip addr, ip link, and ip -s link
• route - show / manipulate the IP routing table (tldr, die, manned)
  • replaced by ip route
• iptables - administration tool for IPv4/IPv6 packet filtering and NAT (tldr, die, manned)
  • ip6tables - administration tool for IPv6 packet filtering and NAT (die, manned)
• ipset - administration tool for IP sets (tldr, die, manned)
• tc - show / manipulate traffic control settings (die, manned)

Remote Administration

• ssh - OpenSSH SSH client (remote login program) (tldr, die, manned)
  • scp - secure copy (remote file copy program) (tldr, die, manned)
  • sftp - secure file transfer program (tldr, die, manned)
  • ssh-agent - authentication agent (tldr, die, manned)
    • ssh-add - adds RSA or DSA identities to the authentication agent (tldr, die, manned)
  • ssh-keygen - authentication key generation, management and conversion (tldr, die, manned)
• telnet - user interface to the TELNET protocol (tldr, die, manned)

Transfer

• wget - non-interactive network downloader (tldr, die, manned)
• curl - transfer a URL (tldr, die, manned)
  • curl -O - download a file
• ftp - Internet file transfer program (tldr, die, manned)

DNS/WHOIS

• dig - DNS lookup utility (tldr, die, manned)
• host - DNS lookup utility (tldr, die, manned)
• nslookup - Internet name servers interactively (tldr, die, manned)
• hostname - show or set the system's host name (tldr, die, manned)
  • hostname -I - all addresses for the host
  • hostname -i - addresses for the host name
  • domainname - show or set the system's NIS/YP domain name (die, manned)
  • dnsdomainname - show the system's DNS domain name (die, manned)
• whois - client for the whois service (tldr, die, manned)

Investigation/Discovery/Exploration

• ping - send ICMP ECHO_REQUEST to network hosts (tldr, die, manned)
  • ping6 (IPv6) (tldr, die, manned)
• ss - another utility to investigate sockets (tldr, die, manned)
• netstat - Print network connections, routing tables, interface statistics, masquerade connections, and multicast memberships. This program is mostly obsolete. (tldr, die, manned)
  • replacement for netstat is ss
  • replacement for netstat -r is ip route
  • replacement for netstat -i is ip -s link
  • replacement for netstat -g is ip maddr.
• traceroute - print the route packets trace to network host (tldr, die, manned)
• tracepath - traces path to a network host discovering MTU along this path (tldr, die, manned)
• nc / netcat - arbitrary TCP and UDP connections and listens (tldr, die, manned)
• nmap - Network exploration tool and security / port scanner (tldr, die, manned)
• tcpdump - dump traffic on a network (tldr, die, manned)

Streams/Pipes

• tee - read from standard input and write to standard output and files (tldr, die, manned)
• sed - stream editor for filtering and transforming text (tldr, die, manned)
• awk - pattern scanning and processing language (tldr, die, manned)

Filesystems

Information

• cat /proc/filesystems - list filesystems your kernel supports
• df - report filesystem disk space usage (tldr, die, manned)
• stat -f - display file or file system status (tldr, die, manned)
• findfs - find a filesystem by label or UUID (tldr, die, manned)
• findmnt - list all mounted filesytems or search for a filesystem (tldr, die, manned)

Block Devices

• lsblk - list block devices (tldr, die, manned)
• blkid - command-line utility to locate/print block device attributes (tldr, die, manned)
• blkdiscard - discard sectors on a device (tldr, manned)
• blkzone - run zone command on a device (manned)
• blockdev - call block device ioctls from the command line (manned)
• losetup - set up and control loop devices (tldr, manned)
• raw - bind a Linux raw character device (tldr, manned)
• zramctl - set up and control zram devices (tldr, manned)

Partitions

• fdisk - partition table manipulator for Linux (tldr, die, manned)
  • fdisk -l - display partitions and exit
• cfdisk - display or manipulate a disk partition table (tldr, die, manned)
• parted - a partition manipulation program (tldr, die, manned)
• addpart - tell the kernel about the existence of a partition (tldr, manned)
• resizepart - tell the kernel about the new size of a partition (manned)
• delpart - tell the kernel to forget about a partition (manned)
• partx - tell the kernel about the presence and numbering of on-disk partitions (tldr, manned)
• sfdisk - display or manipulate a disk partition table (manned)

Mounting

• mount - mount a filesystem (tldr, die, manned)
• mountpoint - see if a directory or file is a mountpoint (tldr, manned)
• unmount - unmount a filesystem (tldr, die, manned)

Repair/Create/Check/Debug

• fsck - check and repair a Linux filesystem (tldr, die, manned)
• mkfs - build a Linux filesystem (tldr, die, manned)
• ext2/ext3/ext4
  • mke2fs - create an ext2/ext3/ext4 filesystem (tldr, die, manned)
  • debugfs - ext2/ext3/ext4 file system debugger (tldr, die, manned)
  • e2fsck - check a Linux ext2/ext3/ext4 file system (tldr, die, manned)
  • e2image - Save critical ext2/ext3/ext4 filesystem metadata to a file ([tldr](https://github.com/ tldr-pages/tldr/blob/main/pages/linux/e2image.md), die, manned)
• fsfreeze - suspend access to a filesystem (Ext3/4, ReiserFS, JFS, XFS) (manned)
• fstrim - discard unused blocks on a mounted filesystem (tldr, manned)
• wipefs - wipe a signature from a device (tldr, manned)

Swaps

• mkswap - set up a Linux swap area (tldr, manned)
• swaplabel - print or change the label or UUID of a swap area (manned)
• swapon - start swapping to file/device (tldr, manned)
• swapoff - stop swapping to file/device (tldr, manned)

Files/Directories

Creation

• mkdir - make directories (tldr, die, manned)
  • mkdir -p - make directory and any missing parent directories
• ln - make links between files (tldr, die, manned)
  • link - create a link to a file/directory (tldr, die, manned)
• fallocate - preallocate or deallocate space to a file (tldr, manned)
• mktemp - create a temporary file or directory (tldr, manned)
• mkfifo - make FIFOs (named pipes) (tldr, manned)

Search

• which - shows the full path of (shell) commands (tldr, die, manned)
• whereis - locate the binary, source, and manual page files for a command (tldr, die, manned)
• find - search for files in a directory hierarchy (tldr, die, manned)
• grep - print lines matching a pattern (tldr, die, manned)
• look - display lines beginning with a given string (manned)
• namei - follow a pathname until a terminal point is found (tldr, manned)

Move/Rename/Copy

• mv - move (rename) files/directories (tldr, die, manned)
  • rename - rename multiple files at once (tldr, die, manned)
• cp - copy files/directories (tldr, die, manned)
  • dd - convert and copy a file (tldr, die, manned)
  • install - copy files and set attributes (tldr, manned)
• hardlink - link multiple copies of a file (manned)

Removal/Shredding

• rm - remove files/directories (tldr, die, manned)
  • unlink - call the unlink function to remove the specified file (tldr, manned)
• rmdir - remove empty directories (tldr, die, manned)
• shred - overwrite a file to hide its contents, and optionally delete it (tldr, die, manned)
• truncate - shrink or extend the size of a file to the specified size (tldr, manned)

Information

• ls - list directory contents (tldr, die, manned)
  • dir - list directory contents (same as ls -Cb)
  • vdir - list directory contents (same as ls -lb)
  • dircolors - set up color for ls
• lsof - list open files (tldr, die, manned)
• stat - display file or file system status (tldr, die, manned)
• basename - strip directory and suffix from filenames (tldr, die, manned)
• dirname - strip non-directory suffix from file name (tldr, die, manned)
• pathchk - check whether file names are valid or portable (tldr, manned)
• pwd - print name of current/working directory (tldr, die, manned)
• du - estimate file space usage (tldr, die, manned)
• fincore - count pages of file contents in core (manned)
• wc - print newline, word, and byte counts for each file (tldr, die, manned)
• file - determine file type (tldr, die, manned)
• test - check file types and compare values (tldr, manned)

Permissions/Locks/Timestamps

• touch - change file timestamps (tldr, die, manned)
  • touch -m - update the modification timestamp
• chmod - change file mode bits (tldr, die, manned)
• chown - change file owner and group (tldr, die, manned)
• chgrp - change group ownership (tldr, die, manned)
• flock - manage locks from shell scripts (tldr, manned)
• lslocks - list local system locks (tldr, manned)
• chattr - change file attributes on a Linux file system (tldr, die, manned)
• lsattr - list file attributes on a Linux second extended file system (tldr, die, manned)

Viewing

• less - Less is a program similar to more, but which allows backward movement in the file as well as forward movement. (tldr, die, manned)
  • lesskey specify key bindings for less (die, manned)
• cat - concatenate files and print on the standard output (tldr, die, manned)
  • tac - concatenate and print files in reverse (tldr, die, manned)
• tail - output the last part of files (tldr, die, manned)
• head - output the first part of files (tldr, die, manned)
• xxd - make a hexdump or do the reverse (tldr, die, manned)
• hexdump - display file contents in hexadecimal, decimal, octal, or ascii (tldr, manned)
• od - dump files in octal and other formats (tldr, manned)

Text Manipulation

• rev - reverse lines characterwise (tldr, manned)
• uniq - report or omit duplicate lines (tldr, die, manned)
• tr - translate or delete characters (tldr, die, manned)
• cut - remove sections from each line of files (tldr, die, manned)
• paste - merge lines of files (tldr, die, manned)
• sort - sort lines of text files (tldr, die, manned)
  • comm - compare two sorted files line by line (tldr, die, manned)
  • tsort - perform topological sort (tldr, die, manned)
• shuf - generate random permutation (tldr, manned)
• join - join lines of two files on a common field (tldr, die, manned)
• fmt - simple optimal text formatter (tldr, die, manned)
• fold - wrap each input line to fit in specified widt (tldr, die, manned)
• expand - convert tabs to spaces (tldr, die, manned)
• unexpand - convert spaces to tabs (tldr, die, manned)
• column - columnate lists (tldr, die, manned)
  • (printf "PERM LINKS OWNER GROUP SIZE MONTH DAY HH:MM/YEAR NAME\n" \ -l | se> ; ls -l | sed 1d) | column -t
• colrm - remove columns from a file (tldr, die, manned)
• nl - number lines of files (tldr, die, manned)
• split - split a file into pieces (tldr, manned)
• csplit - split a file into sections determined by context lines (tldr, die, manned)

Comparison

• diff - compare files line by line (tldr, die, manned)
• cmp - compare files byte by byte (tldr, die, manned)

Checksums/Message Digests/Hashes

• chksum - checksum and count the bytes in a file (tldr, die, manned)
• sha512sum - compute and check SHA512 message digest (tldr, die, manned)
• sha384sum - compute and check SHA384 message digest (tldr, die, manned)
• sha256sum - compute and check SHA256 message digest (tldr, die, manned)
• sha224sum - compute and check SHA224 message digest (tldr, die, manned)
• sha1sum - compute and check SHA1 message digest (tldr, die, manned)
• b2sum - compute and check BLAKE2 message digest (tldr, manned)
• md5sum - compute and check MD5 message digest (tldr, die, manned)

Encoding/Decoding

• base32 - base32 encode/decode data and print to standard output (tldr, manned)
• base64 - base64 encode/decode data and print to standard output (tldr, die, manned)

Encryption/Decryption

• gpg - OpenPGP encryption and signing tool (tldr, die, manned)

Compression/Decompression/Backups/Archives

• rsync - a fast, versatile, remote (and local) file-copying tool (tldr, die, manned)
• logrotate - rotates, compresses, and mails system logs (die, manned)
• tar (tape archiver) - an archiving utility (tldr, die, manned)
  • tar -cf archive.tar foo bar - create archive.tar with files foo and bar
  • tar -tvf archive.tar - list all files in archive.tar
  • tar -xf - extract all files from archive.tar
• gzip - compress files using Lempel-Ziv coding (LZ77) .gz (tldr, die, manned)
  • gunzip - expand files (tldr, die, manned)
  • zless - file perusal filter for crt viewing of compressed text (tldr, die, manned)
  • zgrep - search possibly compressed files for a regular expression (tldr, die, manned)
  • zdiff - compare compressed files line by line (die, manned)
  • zcmp - compare compressed files byte by byte (die, manned)
  • zcat - uncompresses either a list of files on the command line or its standard input and writes the uncompressed data on standard output. identical to gunzip -c (tldr, die, manned)
• bzip2 - a block-sorting file compressor (tldr, die, manned)
  • bunzip2 - decompresses all specified files (die, manned)
  • bzcat - decompresses all specified files to the standard output (die, manned)
  • bzless - file perusal filter for crt viewing of bzip2 compressed text (die, manned)
  • bzgrep - search possibly bzip2 compressed files for a regular expression (tldr, die, manned)
  • bzdiff - compare bzip2 compressed files (die, manned)
• zip - package and compress (archive) files (tldr, die, manned)
  • unzip - list, test and extract compressed files in a ZIP archive (tldr, die, manned)
  • zipinfo - list detailed information about a ZIP archive (tldr, die, manned)
  • zipgrep - search files in a ZIP archive for lines matching a pattern (tldr, die, manned)
• cpio - copy files to and from archives (tldr, die, manned)

Special Utilities

• bc - an arbitrary precision calculator language (tldr, manned)
• numfmt - convert numbers from/to human-readable strings (tldr, manned)
• yes - output a string repeatedly until killed (tldr, manned)
• seq - print a sequence of numbers (tldr, die, manned)
• expr - evaluate expressions (tldr, die, manned)
• factor - factor numbers (tldr, die, manned)
• uuidgen - create a new UUID value (tldr, manned)
• uuidparse - a utility to parse unique identifiers (manned)
• mcookie - generate magic cookies for xauth (tldr, manned)

Bash Builtin Commands

https://www.gnu.org/software/bash/manual/html_node/Builtin-Index.html

Special Parameters

https://www.gnu.org/software/bash/manual/html_node/Special-Parameters.html

• $* - Expands to the positional parameters, starting from one using $IFS
• $IFS - input field separator
• $@ - Expands to the positional parameters, starting from one
• $# - Expands to the number of positional parameters in decimal
• $? - Expands to the exit status of the most recently executed foreground pipeline
• $$ - Expands to the process ID of the shell
• $! - Expands to the process ID of the job most recently placed into the background
• $0 - Expands to the name of the shell or shell script
• $1, $2, ... - Expands to position parameter

Daemons

• init - upstart process management daemon (die)
• inetd - Internet service daemon (die)
• atd - run jobs queued for later execution (die)
• crond - daemon to execute scheduled commands (die)
• useraud - user authentication daemon (die)
• fingerd - remote user information server (die)
• ntpd - Network Time Protocol (NTP) daemon which sets and maintains the system time of day in synchronism with Internet standard time servers (die)
• sshd - OpenSSH SSH daemon for accepting incoming client connections (die)
• httpd - Apache Hypertext Transfer Protocol Server (die)
• mountd - NFS mount daemon (die)
• git daemon - a really simply server for git daemons (die)
• telnetd - DARPA telnet protocol server (die)
• ftpd - DARPA Internet File Transfer Protocol server (die)
• uuidd - UUID generation daemon (tldr, manned)

A subset of the list of currently running processes without a tty will contain most currently running daemons:

ps -eo 'tty,pid,pgid,user,group,args,etime,pcpu' | grep ^?

References

• https://manned.org/
• https://github.com/tldr-pages/tldr/
• https://www.gnu.org/software/bash/manual/
• https://linux.die.net/man/
• https://en.wikipedia.org/wiki/Util-linux
• https://en.wikipedia.org/wiki/List_of_GNU_Core_Utilities_commands