Linux Commands

Command	Description	example	'man' page
`cat`	conCATonate - also outputs files to the terminal (or other file with redirect)	`cat /var/log/messages` this will output the messages file to the terminal	https://man7.org/linux/man-pages/man1/cat.1.html
`cd`	Change Directory	`cd Documents` Changes to the directory "Documents"	https://man7.org/linux/man-pages/man1/cd.1p.html
`chmod`	For changing the permissions on files/folders etc	`chmod u+x app.bin` This will allow the `u`ser to e`x`ecute the file	https://www.man7.org/linux/man-pages/man1/chmod.1.html
`chown`	For changing the user and/or group that the file belongs to	`chown admin:docker docker-compose.yml` This will set the ownership of docker-compose.yml to the user called admin and the group docker.	https://www.man7.org/linux/man-pages/man1/chown.1.html
`dmesg`	Used to examine or control the kernel ring buffer	`dmesg -H` Displays the kernel ring buffer with human readable timestamping/delta time	https://man7.org/linux/man-pages/man1/dmesg.1.html
`dmidecode`	A tool for dumping a computer's DMI (some say SMBIOS ) table contents in a human-readable format. This table contains a description of the system's hardware components, as well as other useful pieces of information such as serial numbers and BIOS revision	`dmidecode -s system-serial-number` Retrieves the serial number/service tag from a motherboard	https://linux.die.net/man/8/dmidecode
`file`	Tests each argument in an attempt to classify it. There are three sets of tests, performed in this order: filesystem tests, magic tests, and language tests. The first test that succeeds causes the file type to be printed	`file /usr/bin/python3.10` outputs `/usr/bin/python3.10: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, BuildID[sha1]=03f0f6b8facea0ce26c35eae211a43b7a00c170b, for GNU/Linux 3.2.0, stripped`	https://linux.die.net/man/1/file
`find`	GNU find searches the directory tree rooted at each given file name by evaluating the given expression from left to right, according to the rules of precedence (see section OPERATORS), until the outcome is known (the left hand side is false for and operations, true for or), at which point find moves on to the next file name.	`find ./ -name grub` Finds a file called "grub" in the current directory	https://linux.die.net/man/1/find
`firewall-cmd`	The command line client of the `firewalld` daemon. It provides an interface to manage the runtime and permanent configurations. Often found running on Redhad based distributions	`firewall-cmd --add-port=443/tcp` Opens port 443 for TCP connections at a run-time level. Change will be lost at reboot or firewall reload	https://firewalld.org/documentation/man-pages/firewall-cmd.html
`grep`	search for matching pattern, can be used in combination with 'cat' for example	`cat /var/log/messages` \| `grep warning` this will search the 'messages' file for the pattern 'warning'	https://man7.org/linux/man-pages/man1/grep.1.html
`groupadd`	Used to add groups to the system	`groupadd cheese` Adds a group called "cheese"	https://linux.die.net/man/8/groupadd
`groupdel`	Used to remove groups from the system	`groupdel cheese` Removes a group called "cheese"	https://linux.die.net/man/8/groupdel
`groupmod`	Used to change details for a group already on the system	`groupmod -n fromage cheese` Changes the group name from "cheese" to "fromage"	https://linux.die.net/man/8/groupmod
`ip`	show / manipulate routing, devices, policy routing and tunnels	`ip a` This will show the status of all networking devices	https://linux.die.net/man/8/ip
`iptables`	Administration tool for IPv4 packet filtering and NAT. Is used to set up, maintain, and inspect the tables of IP packet filter rules in the Linux kernel.	`iptables -A INPUT -p tcp --dport 443 -j ACCEPT` Modifies the packet filter to accept incoming packets on port 443 (on all iterfaces).	https://linux.die.net/man/8/iptables
`iscsiadm`	The iscsiadm utility is a command-line tool allowing discovery and login to iSCSI targets, as well as access and management of the open-iscsi database.	`iscsiadm -m discovery -t sendtargets -p <ip>:3260` This will ask the server at the given IP to show what targets (portals) are available	https://linux.die.net/man/8/iscsiadm
`ln`	Used to create links between files	`ln -s /path/to/target /link/file` This will create a symbolic link between '/link/file' and '/path/to/target'. This can either be files or directories.	https://linux.die.net/man/1/ln
`ls`	list directory	`ls /home/user` this will list out the contents of the users home directory	https://man7.org/linux/man-pages/man1/ls.1.html
`lspci`	list PCI devices connected to machine. Use with verbose option (`-v` or `-vv` or `-vvv`) for useful information		https://linux.die.net/man/8/lspci
`man`	Used to load a manual for a command in a text shell	`man ls` Will load the manual for the `ls` command	https://man7.org/linux/man-pages/man1/man.1.html
`passwd`	Used to change or set passwords for accounts	`passwd floki` Will prompt the user, if allowed, to set the password for the 'floki' account.	https://linux.die.net/man/1/passwd
`pinfo`	A program used for viewing info files, developed by the GNU project	`pinfo tar` Displays the tar info page.	https://linux.die.net/man/1/pinfo
`realpath`	Converts each filename argument to an absolute pathname, which has no components that are symbolic links or the special . or .. directory entries.	`realpath .bashrc` returns `/home/user/.bashrc`	https://linux.die.net/man/1/realpath
`rm`	Removes files or directories	`rm file1 file2 file3` This command will remove file1, file2 and file3.	https://linux.die.net/man/1/rm
`sed`	Stream EDitor. For filtering and transforming text	`sed -i 's/pc-i440fx-rhel7.0.0/pc-i440fx-7.2/g' virtual_machine.xml` Replaces "pc-i440fx-rhel7.0.0" with "pc-i440fx-7.2". Search/replace pattern takes the form s/regex/replacement/.	https://linux.die.net/man/1/sed
`scp`	secure copy between hosts using SSH	`scp user01@host1:file user01@host2:file` copy file from host1 to host2	https://man7.org/linux/man-pages/man1/scp.1.html
`ssh`	A program to login to to a remote host using a Secure SHell	`ssh user@host02` Creates a secure, encrypted link between current host and host02 and attempts to login as "user"	https://linux.die.net/man/1/ssh
`su`	Log in as another user without having to log out. If you are not the 'root' user, the password fo the target user will be required.	`su - user03` logs in as 'user03' and loads the environment variables for that user. If the '-' is ommitted, then the environment variables are not loaded	https://linux.die.net/man/1/su
`sudo`	Usually used to execute a command as a user with escalated priviledge	`sudo apt update` the `apt` command cannot be run under ordinary user rights and must be run as a privildged user (e.g. root).	https://linux.die.net/man/8/sudo
`smartctl`	smartctl controls the Self-Monitoring, Analysis and Reporting Technology (SMART) system built into many ATA-3 and later ATA, IDE and SCSI-3 hard drives. The purpose of SMART is to monitor the reliability of the hard drive and predict drive failures, and to carry out different types of drive self-tests.	`smartctl -i /dev/sda` Ouputs drive info for `/dev/sda` `smartctl -a /dev/sda -d sat+megaraid,00` Gets all info from a disk behind a PERC controller where `/dev/sda` is the array and `00` is the first disk in that array	https://linux.die.net/man/8/smartctl
`strings`	For each file given, GNU strings prints the printable character sequences that are at least 4 characters long (or the number given with the options below) and are followed by an unprintable character. By default, it only prints the strings from the initialized and loaded sections of object files; for other types of files, it prints the strings from the whole file.	`strings .face` outputs `<svg version="1" viewBox="0 0 512 512" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink"><defs><linearGradient id="b" x1="211.18" x2="349.73" y1="370.82" y2="232.27" gradientTransform="matrix(1.0606 0 0 1.0606 -62.005 -15.504)" gradientUnits="userSpaceOnUse">......`	https://linux.die.net/man/1/strings
`systemctl`	`systemctl` may be used to introspect and control the state of the "systemd" system and service manager	`systemctl start sshd` This will start the `sshd` daemon	https://www.man7.org/linux/man-pages/man1/systemctl.1.html
`tar`	GNU 'tar' saves many files together into a single tape or disk archive, and can restore individual files from the archive.	`tar -cf archivename.tar /files-to-include` Creates an archive called "archivename.tar" with the file "files-to-include".	https://linux.die.net/man/1/tar
`tcpdump`	Prints out a description of the contents of packets on a network interface	`tcpdump -i enp0s3` Prints packets captured on enp0s3 to the console	https://linux.die.net/man/8/tcpdump
`useradd`	Command used to add users to the system. By default it will configure new users' home ddirectories	`useradd thor` Adds a user called 'thor' with the default settings	https://linux.die.net/man/8/useradd
`userdel`	Used to delete users from a system	`userdel loki` Delets 'loki' from the system, home directory may still remain	https://linux.die.net/man/8/userdel
`usermod`	Used to modify existing users	`usermod -L huginn` This will lock the account 'huginn' preventing any login	https://linux.die.net/man/8/usermod
`vim`	A text editor that is upwards compatible to Vi. It can be used to edit all kinds of plain text. It is especially useful for editing programs.	`vim ~/newfile` Runs vim and opens "newfile" or creates "newfile" if "newfile" does not exist	https://linux.die.net/man/1/vi
`wget`	Wget is a free utility for non-interactive download of files from the Web. It supports HTTP , HTTPS , and FTP protocols, as well as retrieval through HTTP proxies.	`wget -m https://dell.com` Option "-m" will mirror the target URL and pull down all associated files, including CSS files etc	https://linux.die.net/man/1/wget

Command	Use
`cd dirName`	Moves fromthe current working directory to the directory named "dirName", supposing that "dirName" is a valid directory inside the current directory
`cd ~`	Changes from wherever you are in the filesystem back to your home directory. Simply typing `cd` can usually be used for the same purpose
`cd -`	This will take you back to the last working directory. E.g. if you were in /home/user/Documents and did `cd ../Downloads` to change to the "Downloads" directory, typing `cd -` will take you back to the "Documents" directory
`cd ..`	This will take you to one directory above the current working directory
`cd ../..`	This will take you to two directoryies above the current working directory
`cd /`	This will take you to the root of the file system
`cd -al`	This will list all files (including hidden files) with a the long listing to show all the file permissions etc
`cd /bin`	From wherever you are in the filesystem, this will take you to the "/bin" directory

Command	Explanation
`chmod u+x file`	Adds the executable permission to file
`chmod g-rw file`	Removes read/write permissions from file for the group
`chmod o-rwx file`	Removes read/write/execute permissions from file for users that are not the user or in the group
`chmod ug+rwx`	Adds read/write/execute permissions to file for the user and group members

Command	Explanation
`chown root:wheel file`	Changes the ownership of file to the 'root' user and the 'wheel' group
`chown user1: file`	Changes the ownership of file to the 'user1' user and the 'user1' group. Leaving a trailing colon makes the command assume that the user is the same as the group name

Command	Explanation
`firewall-cmd --get-services`	Lists out the 'services' available. These are predefined rules for services such as http, https, ssh and so on.
`firewall-cmd --add-service=http`	Opens the ports associated with the 'http' predefined service at runtime on the default zone (change will be lost at reboot or firewall reload)
`firewall-cmd --permanent --add-port=139/tcp`	Opens port 139 for TCP connections on the default zone and ensures that the change will be loaded after a reboot.
`firewall-cmd --reload`	This will reload the firewall from the permanent settings, any unsaved runtime changes will be lost
`firewall-cmd --state`	Checks the firewall status.
`firewall-cmd --list-all`	Lists all firewall rules and zones.
`firewall-cmd --zone=public --list-all`	Lists all rules in the 'public' zone.
`firewall-cmd --remove-service=http --permanent`	Removes the permanent HTTP service rule.

option	use
`-i`	Makes the search case insensitive
`-v`	Inverts the search - finds things that do not match the pattern
`pattern1\\\|patern2`	searchers for "patern1" or "patern2"

Command	Explanation
`ln /path/to/target /path/to/link`	This creates a hard link. If the target file is deleted, then there will still be a hard link to /path/to/link. In order for the file to be effectively removed from the file systems all hardlinks must be deleted.
`ln -s /path/to/target /path/to/link`	This will create a symbolic/soft link from a specified path back to the target. Oftentimes this will be transparent to applications. If the link is deleted, the file remains intact in at its original location. If the file at /path/to/target is deleted, then the symbolic link will remain in place, but will link to nothing.

Command	Explanation
`lspci -v`	Lists PCI(e) devices in a verbose manner. You can increase the verbosity by adding up to two more `v`, e.g. `lspci -vv` or `lspci -vvv`
`lspci -d :1042`	Lists devices of a certain class. In this example, this will list SCSI storage devices.
`lspci -nn`	Lists PCI vendor and device codes as both numbers and names. You can then use these with the `-d` option listed above.
`lspci -t`	Lists PCI(e) devices in a tree view, can be used in conjuction with verbosity options for more detail.

Navigation	pinfo	man
Scroll forward (down) one screen	PageDown or Space	PageDown or Space
Scroll backward (up) one screen	PageUp or b	PageUp or b
Display the directory of topics	d	-
Scroll forward (down) one half-screen	-	d
Display the parent node of a topic	u	-
Display the top (up) of a topic	HOME	g
Scroll backward (up) one half-screen	-	u
Scroll forward (down) to next hyperlink	DownArrow	-
Open topic at cursor location	Enter	-
Scroll forward (down) one line	-	DownArrow or Enter
Scroll backward (up) to previous hyperlink	UpArrow	-
Scroll backward (up) one line	-	UpArrow
Search for a pattern	/string	/string
Display next node (chapter) in topic	n	-
Repeat previous search forward (down)	/ then Enter	n
Display previous node (chapter) in topic	p	-
Repeat previous search backward (up)	-	N
Quit the program	q	q

Command	Use
`rm file1`	Removes file1. Can add multiple file names here to be removed.
`rm -r dir`	Recurse in to dir and remove dir
`rm -r $(find -maxdepth 1 -type d)`	This will find directories (`-type d` option) and then delete them without recursing in to subdirectories (`-maxdepth 1` option). This is using a combination of the `find` command and passing the output from that to the `rm` command

Command	Use
`scp -o ProxyJump=user@host2:22 user@host1:/path/to/file user@host3:/path/to/destination`	Copy a file from host1 to host3 using host2 as a proxy

Command	Use
`ssh host02`	Open a secure link between current host and host02. As a user is not specified, the user on the current host will be used
`ssh -X user@host02`	Opens a secure link between current host and host02, attempts to begin logon as "user" and enables X-forwarding
`ssh -i ~/.ssh/hostkey user@host02`	The `-i` option specifies an "indenty file" (or key file) to use to connect to host02 and attempt to login as "user". For information on generating a key file, please see ssh-key-gen
`ssh -L 5900:localhost:5901 user@host02`	Creates an ssh tunnel from one machine to another. In this example, connecting to port 5900 on your local machine will forward to port 5901 on the remote system

Command	Use
`net-list`	List the virtual networks on the host
`net-dhcp-leases <network>`	List the DHCP leases on `<network>` (which is a required argument)
`net-destroy default`	Deletes the "default" network
`net-define br0-network.xml`	Creates the "br0-network" from an xml file
`net-start br0-network`	Starts the "br0-network
`list [--all]`	Lists domains on the host. If `--all` is omitted, then it will list the running domains (virtual machines/containers)
`dominfo <domain>`	Lists basic information about a domain. Domain can either be the domain ID or name (these can both be found using the `list` command)
`define virtualmachine.xml`	Creates a virtual machine from an xml file

Command	Use
`qemu-img info /path/to/image.qcow2`	Gives basic information about "image.qcow2"
`qemu-img create -f qcow2 image.qcow2 20G`	Creates an image named "image.qcow2" with size of 20 gigs with `-f`ormat "qcow2".
`qemu-img resize image.qcow2 30G`	This will resize the image to 30 gigs. If the image is larger than 30G, it you will receive a warning and it will suggest that you use the `--shrink` option to shrink the image if that is what you want to do. Instead of specifying the size of the disk, you can also add on a set number of bytes, e.g. +10G would add 10 gigs to the image. Should not be used on a "live" image, the VM should be shut off
`qemu-img convert -O qcow2 vmwareimage.vmdk qemuimage.qcow2`	This will convert from VMware format (vmdk) to QEMU format (qcow2). Though it should be noted that QEMU can work with VMDK images.

¶ Cheatsheet

¶ Command Examples and more information

¶ General Commands

¶ cd

¶ chmod

¶ chown

¶ firewall-cmd

¶ grep

¶ ip

¶ ln

¶ lspci

¶ nmcli

¶ man

¶ pinfo

¶ rm

¶ rsync

¶ scp

¶ ssh

¶ virsh

¶ qemu-img

¶ Cheatsheet

¶ Command Examples and more information

¶ General Commands

¶ cd

¶ chmod

¶ chown

¶ firewall-cmd

¶ grep

¶ ip

¶ ln

¶ lspci

¶ nmcli

¶ man

¶ pinfo

¶ rm

¶ rsync

¶ scp

¶ ssh

¶ Virtualisation related commands

¶ QEMU related

¶ virsh

¶ qemu-img