CS469 - Linux and Unix Administration and Networking

Commands:

Basic commands you should know how to use:

Command	What it does
`man`	Read the online manual pages
`ls`	List files
`cd`	Change directory
`cp`	Copy files
`mv`	Rename / move files
`rm`	Remove file
`mkdir`	Make a directory
`rmdir`	Remove empty directory
`chmod`	Set permissions on file or files.
`chown`	Set ownership on files.
`chgrp`	Set group ownership on files.
`touch`	Updates last access and modification times of files, creating new files if necessary.
`getfacl`	Display the ACLs on a file or files
`setfacl`	Set/update the ACLs on a file or files
`ln`	Make links (symbolic or hard) between files.
`cat`	Concatenate files
`more/less/most`	Paginate output of files
`grep`	Search for pattern in files.

Editors


`kate`	The best Unix text editor
`jove`	The best text-mode Unix text editor
`vi`	The default Unix text editor for some reason
`emacs`	A heavy-weight text-mode text editor
`nano`/`pico`	A simple text editor
`ne`	A Nice Editor

Misc file commands commands:

Command	What it does
`df`	Displays mounted file-systems and information about them
`umask`	Set/show the default file/directory permissions creation mask.
`readlink`	Print the value of a symbolic link.
`realpath`	Print the real resolved path from the path given.
`head`	Print first (10) lines in a file.
`tail`	Print last (10) lines in a file.
`zcat / zgrep / gzip`	Performs ops on gzipped files.
`file`	Identifies the type of a file file is.
`find`	Search for files in a directory hierarchy
`locate`	Search for files indexed in a location database (much faster than find)
`tree`	Display files and directories in a depth indented listing
`sed`	Stream editor for filtering and transforming text.
`printenv`	Displays the current environment.
`dd`	Convert and copy files
`init/telinit`	Change runlevel.
`runlevel`	Displays the current runlevel
`shutdown`	Halt (-h) or reboot (-h) the system.

Common scripting utilities and programs:

Command	What it does
`true`	Always succeeds (true)
`false`	Always fails (false)
`sort`	Sort the lines in a file.
`uniq`	Filters out adjacent matching lines.
`basename`	Strip the directory name [and suffix] from a filename.
`dirname`	Strip last component from filename.
`tr`	Translate or delete characters
`tac`	Cat files in reverse
`colrm`	Remove columns from a file.
`cut`	Remove sections from each line of a file.
`tee`	Read from stdin and write to stdout and files
`env`	Run a program in a modified environment.
`date`	Print or set system date and time.

Bash built-ins:

Command	What it does
`declare`	Declares variables of a specific type
`let`	Defines integer variables, performs C like arithmetic expressions.
`local`	Makes variables local to a function, otherwise variables are global by default.
`export`	Makes a variable part of the environment
`unset`	Unset the variable (default or -v) or function (-f).
`alias`	Creates an command alias.
`bg`	Continues a stopped process in the background.
`fg`	Brings a job to the foreground.
`jobs`	Lists jobs, both running and stopped.
`echo`	Prints to the output, or a newline if strings is omitted.
`printf`	Like the C printf function
`read`	Reads a line of text and splits it according to IFS and assigns words the variables listed.
`test`	Same as [...] and mostly [[...]]
`source` / `.`	Reads and executes in the current shell.
`ulimit`	Set resource limits.

Process and Library commands:

Command	What it does
`ps`	Report snapshot of current processes
`pstree`	View processes in a tree like format
`top/htop`	View processes continously
`kill`	Send a signal to a process or processes.
`killall`	Send a signal to a process or processes by name
`pgrep`	Look up processes based on name and other attributes.
`pkill`	Signal processes based on name and other attributes.
`ldconfig`	Maintains links to shared libraries and updates the linker cache files
`ldd`	Lists the shared library/objects used by a particular program.
`nm`	lists symbols from an object.
`ar`	Create/modify and extract from archives (.a files).
`strace`	Trace syscalls made by a running executable.
`nice`	Start a program at a specific niceness
`renice`	Set the niceness of a running process.
`ionice`	Get/Set I/O scheduling class and priority
`limit/ulimit`	Set resource limits. (shell builtins)

File-systems and associated commands

Command	What it does
`fdisk`	Partition a disk
`parted`	Partition a disk (supports GPT)
`mkswap`	Initialize a swap parition or file
`swapon`	Enable swapping on devices
`swapoff`	Disable swapping
`swaplabel`	Show/set swap label
`mount`	Maps a filesystem into the directory hierarchy.
`umount`	Removes a file-system from the directory hierarchy (un-mounts a filesystem.)
`fuser`	Display processes (& users -u) using files, filesystems (-m) or sockets (-n).
`lsof`	Like fuser, but more. Lists open files for all processes.
`mkfs.*`	Make a filesystem
`mke2fs`	Make an ext[234] filesystem.
`fsck.*`	Check and repair a file-system
`e2fsck`	Check and repair a Linux ext[234] filesystem.
`badblocks`	Check device for bad blocks.
`e2label`	Display or change the label on a ext* filesystem.
`tune2fs`	Tune the file-system parameters on ext* file-systems.
`mknod`	Make a device file
`iostat`	Display CPU and disk I/O stats.
`vmstat`	Display virtual memory statistics.
`mdadm`	Linux MD (RAID) administration tool

User management:

Command	What it does
`useradd`	Adds a user to the system
`userdel`	Delete a user
`usermod`	Modify user
`adduser`	Script wrapper to useradd
`newusers`	Add users in bulk
`chfn`	Change finger (gecos) information.
`chsh`	Change default login shell.
`passwd`	Change password for a user.
`chpasswd`	Change passwords in bulk
`chage`	Change password expiration for a user.
`groupadd`	Add a group to the system
`groupmod`	Modify a group on the system
`groupdel`	Delete a group on the system
`gpasswd`	Change a group password
`vipw`	Edit passwd / shadow (`-s`) file
`vigr`	Edit group / gshadow (`-s`) file
`sudo`	Execute a command or start an interactive shell as another user (by default root.)
`su`	Switch user
`newgroup`	Switch group
`sg`	Like newgroup but accepts a command
`id`	Display current user/uid and group names/gid's.
`groups`	Display current group memberships
`last`	Display last logins in reverse order.
`sac / ac`	System login accounting, displays login accounting (usage.)
`finger/w/who/users`	Display who is currently logged in.

Log files:

Command	What it does
`klogd`	System daemon that logs kernel messages (usually through the syslog facility.)
`dmesg`	Prints kernel messages to the console.
`syslogd`	System logging daemon
`logger`	Command line tool to log messages to the syslog facility.
`logrotate`	Rotate/compress/mail system logs

Quotas:

Command	What it does
`quotacheck`	Check and update quota files.
`quotaon`	Enable quotas on a file-system or (`-a`) all file-systems.
`quotaoff`	Turn quotas off on a filesystem or (`-a`) all file-systems.
`quota`	Display user or group quota
`edquota`	Edit user/group quota
`setquota`	Command line quota editor
`warnquota`	Send email to users over quota
`repquota`	Quota report
`quotastats`	Quota statistics

MySQL / MariaDB commands:

Command	What it does
`mysql`	The MySQL/MariaDB client command
`mysqldump`	Dumps MySQL / MariaDB databases as SQL
`mysqlshow`	Displays a list of MySQL/ MariaDB databases

Networking commands:

Command	What it does
`ssh`	Secure shell to another computer.
`scp`	Copy files using ssh
`sftp`	Secure FTP client
`rsync`	Like scp, but only copies changed files.
`ssh-keygen`	Authentication key generation, management and conversion
`ssh-copy-id`	Install your public key in a remote machine's authorized_keys
`nc`	(netcat) TCP/IP swiss army knife
`curl`	Transfer/get a URL to your local machine via the command line.
`wget`	Non-interactive network down-loader
`arp`	Manipulate and display ARP cache
`hostname`	Set (requires root) or show the systems hostname
`dig`	Another DNS lookup util
`host`	DNS lookup util
`nslookup`	Yet another DNS lookup util (older, almost deprecated.)
`ifconfig`	Configure a network interface (being deprecated)
`ip`	Show/manipulate routing, devices, policy routing and tunnels.
`route`	Print and set routes
`routel`	List routes
`traceroute`	Show routes taken from host to destination.
`ping`	Send ICMP echo's to a machine.
`iptables`	Setup firewall rules
`openssl`	SSL/TLS certificate and key management + misc SSL commands

Misc

Wildcards

Wildcards are NOT regular expressions

Wild-card	What it represents
~	Your home directory
~username	usernames home directory
`*`	Matches zero or more characters
`?`	Matches a single character
`[...]`	Matches any single character enclosed in the brackets

Regular Expressions

Regular expressions are not wildcards

File-system


/	The root of the file-system directory (not the root account)
.	The current directory
..	The parent directory
.*	A "hidden" file (not normally listed unless -a option used.)

Location	What goes there
`/bin`	Programs that required at boot time
`/boot`	Location of kernel and boot loader files
`/dev`	Location of the devices files
`/etc`	System wide configuration files
`/lib*`	Program libraries needed by programs at boot time
`/proc`	The process and system configuration pseudo-file-system
`/run`	The runtime files for system services
`/sbin`	Programs (usually used by the administrator) needed at boot time
`/sys`	System information pseudo-filesystem
`/tmp`	Temporary files not guaranteed to be preserved across reboots
`/usr`	Read only data not needed at boot time
`/usr/bin`	Most user programs
`/usr/lib*`	Most of the program libraries
`/usr/local`	Tertiary hierarchy for local system additions
`/usr/sbin`	non-essential system programs (daemons)
`/usr/share`	Shared data
`/var`	Variable data that changes during run-time
`/var/log`	Log files (syslogd and klogd)
`/var/mail`	User mailboxes
`/var/tmp`	Temporary files that are guaranteed to be preserved across reboots

Bash

Invocation: #!/bin/bash
chmod a+x ... to make executable
Pipelines: a | b, a |& b, ! a
Command lists: a ; b, a & b, a && b, a || b
if a; then echo "a was successful"; fi
if ! a; then echo "a failed"; fi
Compound commands:
- ( commands ) (subshell)
- { commands } (local shell)
- (( C-expression )) (as a command, evaluates to true/false)
- [ test-expression ]
- [[ test-expression ]]
I/O redirections:
- < file - reads file as input
- > file - outputs to file, overwriting it
- >> file - Appends to file
- &>, &>> - Outputs/appends both stdout/stderr to file
- Heredocs: <<, <<< string, < <( command )
Quoting:
- single quotes - no expansions
- double quotes - variable expansions
Bash data types: strings, integers, arrays and associative arrays
Variable expansions:
- Basic expansion: $foo, ${foo}
- Array size: ${#foo[*]}
- Default: ${foo:-default}
- $(( expression ))
Command expansion:
- $( expression )
- back-ticks
Functions - how to define them, how to make variables local
Loops:
- while program; do statements; done
- for variable; do statements; done - iterates over the positional parameters
- for variable in words; do statements; done - iterates over words
- for (( init ; test ; inc )) { statements } - C style loop
Conditional:
- if command ; then statements ; fi
- if command ; then statements ; else statements ; fi
- if command ; then statements ; elif statements ; else statements ; fi

Bash special var	What it does
`$?`	Status of the last command run
`$#`	Number of positional parameters
`$1`, $2...	The positional parameters (the command line arguments )
`$*`, `$@`	Expands to the positional parameters ($1 and up )
IFS	The internal field separator
RANDOM	Random number from 0 to 32767
PATH	The colon delimited string of file-system paths to search for programs in

for var in $*; do .. done - Iterates over the positional parameters from $1 up.

Processes and threads

State	What it represents
R	Running: the process is executing in normal user-space.
S	Interruptible Sleep: The process has either given up it's time slice or been pre-empted by the kernel into giving up it's time.
D	Uninterruptible Sleep: The process is waiting on I/O to complete, usually means it is waiting for a kernel system call to return.
T	Stopped: The process execution has been temporarily suspended by a job control signal (SIGSTOP/SIGTSTP) until it is continued (via SIGCONT)
X/Z	Dead or Zombie: The process has completed and has either been reaped (X - should never actually be seen) or is waiting to be reaped (Z).

Attributes
Memory	How much memory the process is using (VSZ - Virtual Size, RSS - Resident Set Size - non-swapped heap+stack, Size - Heap+Stack
FS info	root FS, cwd, umask, etc
I/O Descriptors	Files, IPC, network objects
Namespace	Hierarchy of mounted file-systems
Signal Handlers	+ Signal dispositions
Credentials	Identifying info about process and parents
Scheduling Priority	Niceness: -19 (highest) - 20 (lowest)
Resource Limits
Processor affinity	How closely tied to specific CPUs/Memory
Additional meta info	Start / CPU time / Current state / CPU running on

Misc

Path resolution
Inode information about files (Owner uid/gid, mode (permissions), file-type, size, times (atime, ctime, mtime))
What each part of 'ls -l' output means
- file types: d, -, l
ACLs
Regular expressions
Signals SIGSTOP, SIGKILL cannot be caught blocked or ignored.
Process resource limits