Linux Command Reference

Platform: Ubuntu 24.04 LTS, Bash 5.2, GNU coreutils 9.4. Commands marked GNU may differ on macOS/BSD.

Navigation & System Information

whoami

Field	Detail
OS	All Linux (coreutils)
Description	Prints the effective user name of the current process.
Syntax	whoami
Parameters	--help, --version
Example	whoami
Expected output	student
Equivalent	PowerShell: whoami (prints HOST\user), $env:USERNAME
Common errors	None in practice. Under sudo it prints root, which is expected.
Use case	Confirm the account before administrative work, or during incident triage.
Docs	https://man7.org/linux/man-pages/man1/whoami.1.html

hostname

Field	Detail
OS	All Linux
Description	Shows (or, as root, temporarily sets) the system host name.
Syntax	hostname [-s | -f | -I]
Parameters	-s short name · -f FQDN · -I all IP addresses (Linux)
Example	hostname -I
Expected output	192.168.56.10 10.0.2.15
Equivalent	PowerShell: hostname, $env:COMPUTERNAME
Common errors	hostname -f returning just the short name means DNS//etc/hosts has no FQDN. Use hostnamectl set-hostname for a permanent change.
Use case	Confirm you are on the correct server before a restart.
Docs	https://man7.org/linux/man-pages/man1/hostname.1.html

pwd

Field	Detail
OS	Bash built-in and coreutils
Description	Prints the absolute path of the current working directory.
Syntax	pwd [-L | -P]
Parameters	-L logical (default, keeps symlinks) · -P physical (resolves symlinks)
Example	cd /bin && pwd -P
Expected output	/usr/bin
Equivalent	Get-Location
Common errors	None
Use case	Check location before relative-path operations such as deletes.
Docs	https://man7.org/linux/man-pages/man1/pwd.1.html

ls

Field	Detail
OS	All Linux (coreutils)
Description	Lists directory contents.
Syntax	ls [OPTION]... [FILE]...
Parameters	-l long · -a all/hidden · -h human sizes · -t by time · -S by size · -r reverse · -R recursive · -d the directory itself · -i inode
Example	ls -lht /var/log | head -5
Expected output	-rw-r----- 1 syslog adm 38K Nov 8 09:17 auth.log …
Equivalent	Get-ChildItem (-Force for hidden)
Common errors	ls: cannot open directory '/root': Permission denied, because you need rights on the directory.
Use case	Find the most recently modified log files.
Docs	https://man7.org/linux/man-pages/man1/ls.1.html

uname

Field	Detail
OS	All Linux (coreutils)
Description	Prints kernel and machine information.
Syntax	uname [-a] [-s] [-n] [-r] [-v] [-m] [-o]
Parameters	-a all · -r kernel release · -m architecture · -n node name · -o OS
Example	uname -r
Expected output	6.8.0-48-generic
Equivalent	Get-ComputerInfo -Property OsName,OsVersion,OsArchitecture (Windows), [Environment]::OSVersion
Common errors	Treating the kernel release as the distribution version. Use /etc/os-release for that.
Use case	Check kernel version against a vulnerability advisory.
Docs	https://man7.org/linux/man-pages/man1/uname.1.html

date

Field	Detail
OS	All Linux (GNU coreutils; -d is GNU-specific)
Description	Prints or sets the system date and time; formats and calculates dates.
Syntax	date [-u] [-d STRING] [+FORMAT]
Parameters	-u UTC · -d 'yesterday' arbitrary date · -I[seconds] ISO 8601 · +%F YYYY-MM-DD · +%s epoch
Example	date -u -Iseconds
Expected output	2026-11-08T10:05:43+00:00
Equivalent	Get-Date, (Get-Date).ToUniversalTime(), Get-Date -Format o
Common errors	Forgetting quotes around formats with spaces: date +%F %T fails, date '+%F %T' works.
Use case	Timestamped file names: backup-$(date +%F).tar.gz.
Docs	https://man7.org/linux/man-pages/man1/date.1.html

hostnamectl / timedatectl

Field	Detail
OS	systemd-based distributions (Ubuntu 15.04+)
Description	Query or change host name and OS details / time zone and NTP status.
Syntax	hostnamectl [status | set-hostname NAME] · timedatectl [status | set-timezone ZONE | list-timezones]
Example	timedatectl
Expected output	Time zone: Asia/Kolkata (IST, +0530) … System clock synchronized: yes
Equivalent	Get-TimeZone, w32tm /query /status, Rename-Computer
Common errors	Failed to connect to bus in containers without systemd.
Use case	Fix clock drift that breaks authentication or log correlation.
Docs	https://man7.org/linux/man-pages/man1/timedatectl.1.html

Help & Discovery

man

Field	Detail
OS	Ubuntu (man-db)
Description	Displays the manual page for a command, file format or system call.
Syntax	man [SECTION] PAGE · man -k KEYWORD
Parameters	-k search descriptions (= apropos) · -f one-line description (= whatis)
Example	man 5 passwd
Expected output	The manual page for the /etc/passwd file format, in a pager (q to quit)
Equivalent	Get-Help <cmdlet> -Full
Common errors	No manual entry for X on minimal images: sudo apt install man-db manpages (and unminimize on servers).
Use case	Working on air-gapped servers without internet.
Docs	https://man7.org/linux/man-pages/man1/man.1.html

type / which / help

Field	Detail
OS	Bash built-ins (type, help); which from debianutils
Description	type shows how Bash resolves a name; which shows the executable path; help documents built-ins.
Syntax	type [-a] NAME · which NAME · help BUILTIN
Example	type -a ls
Expected output	ls is aliased to 'ls --color=auto' / ls is /usr/bin/ls / ls is /bin/ls
Equivalent	Get-Command NAME (-All)
Common errors	which cd prints nothing, because cd is a built-in. Use type.
Use case	Detect a malicious alias or a PATH hijack (type -a sudo).
Docs	https://www.gnu.org/software/bash/manual/bash.html#Bash-Builtins

Files & Directories

cd

Field	Detail
OS	Bash built-in
Description	Changes the shell's current directory.
Syntax	cd [DIR | - | ~ | ..]
Example	cd /var/log && cd -
Expected output	cd - prints the directory it returns to, e.g. /home/student
Equivalent	Set-Location (cd); Set-Location - in 6.2+
Common errors	bash: cd: too many arguments (unquoted spaces) · No such file or directory · Permission denied (no x permission on the directory)
Use case	Fast navigation; cd - toggles between two working directories.
Docs	help cd

mkdir

Field	Detail
OS	All Linux (coreutils)
Description	Creates directories.
Syntax	mkdir [-p] [-v] [-m MODE] DIR...
Parameters	-p create parents, no error if existing · -v verbose · -m 750 set permissions
Example	mkdir -pv /tmp/app/{logs,conf}
Expected output	mkdir: created directory '/tmp/app' … '/tmp/app/logs' … '/tmp/app/conf'
Equivalent	New-Item -ItemType Directory -Force (mkdir function on Windows)
Common errors	File exists (add -p) · Permission denied (parent not writable)
Use case	Idempotent setup of application directory trees.
Docs	https://man7.org/linux/man-pages/man1/mkdir.1.html

touch

Field	Detail
OS	All Linux (coreutils)
Description	Creates an empty file, or updates the timestamps of an existing file without changing its content.
Syntax	touch [-c] [-a|-m] [-d DATE] FILE...
Parameters	-c do not create · -a/-m access/modify time only · -d '2026-01-01 09:00' set a specific time
Example	touch report.txt && ls -l report.txt
Expected output	-rw-rw-r-- 1 student student 0 Nov 8 16:02 report.txt
Equivalent	New-Item -ItemType File (new) · (Get-Item f).LastWriteTime = Get-Date (update)
Common errors	Permission denied in directories you cannot write to
Use case	Create marker/lock files; reproduce time-based test conditions.
Docs	https://man7.org/linux/man-pages/man1/touch.1.html

cp

Field	Detail
OS	All Linux (coreutils)
Description	Copies files and directories.
Syntax	cp [-r] [-i|-n] [-v] [-p|-a] [-u] SOURCE... DEST
Parameters	-r recursive · -a archive (preserve all, recursive) · -p preserve attributes · -i prompt · -n no-clobber · -u only newer · -v verbose
Example	sudo cp -a /etc/ssh/sshd_config /etc/ssh/sshd_config.bak.$(date +%F)
Expected output	No output on success (add -v to see 'a' -> 'b')
Equivalent	Copy-Item (-Recurse), robocopy for attribute-preserving copies
Common errors	-r not specified; omitting directory · nested-folder surprise when the destination exists
Use case	Timestamped backups before configuration changes.
Docs	https://man7.org/linux/man-pages/man1/cp.1.html

mv

Field	Detail
OS	All Linux (coreutils)
Description	Moves or renames files and directories.
Syntax	mv [-i|-n] [-v] [-u] SOURCE... DEST
Parameters	-i prompt before overwrite · -n never overwrite · -v verbose · -u only if newer
Example	mv -v app.log app.log.1
Expected output	renamed 'app.log' -> 'app.log.1'
Equivalent	Move-Item, Rename-Item
Common errors	Silent overwrite of an existing destination (use -i/-n) · cannot stat (source missing)
Use case	Manual log rotation; archiving processed files.
Docs	https://man7.org/linux/man-pages/man1/mv.1.html

rm

Field	Detail
OS	All Linux (coreutils)
Description	Removes files and (with -r) directory trees. Permanent: no trash.
Syntax	rm [-i|-I] [-r] [-f] [-v] [--] FILE...
Parameters	-i prompt each · -I prompt once · -r recursive · -f force (no prompts) · -v verbose · -- end of options
Example	rm -Iv *.tmp
Expected output	rm: remove 4 arguments? then removed 'a.tmp' …
Equivalent	Remove-Item (-Recurse, -Force, -WhatIf, -Confirm)
Common errors	Is a directory (needs -r) · Permission denied (no write permission on the parent directory)
Use case	Cleaning build artefacts after previewing with ls.
Docs	https://man7.org/linux/man-pages/man1/rm.1.html

rmdir

Field	Detail
OS	All Linux (coreutils)
Description	Removes empty directories only.
Syntax	rmdir [-p] [-v] DIR...
Example	rmdir -v old-empty-dir
Expected output	rmdir: removing directory, 'old-empty-dir'
Equivalent	Remove-Item DIR (prompts if not empty)
Common errors	Directory not empty, which is the intended safety behaviour
Use case	Safe cleanup scripts that must never delete content.
Docs	https://man7.org/linux/man-pages/man1/rmdir.1.html

file / stat

Field	Detail
OS	All Linux
Description	file identifies content type by inspecting bytes; stat shows full metadata.
Syntax	file FILE... · stat FILE...
Example	file /usr/bin/ls
Expected output	/usr/bin/ls: ELF 64-bit LSB pie executable, x86-64, ...
Equivalent	Get-Item f | Format-List * (metadata); first bytes via Get-Content -Encoding Byte -TotalCount 4 (5.1) / -AsByteStream (7)
Common errors	None common
Use case	Spot executables disguised with document extensions.
Docs	https://man7.org/linux/man-pages/man1/file.1.html · https://man7.org/linux/man-pages/man1/stat.1.html