Random computer tricks

Linux terminal commands

chmod

You would normally use chmod to change the permissions for a file. The chmod command can use symbols u (user that owns the file), g (the files group) , and o (other users) and the permissions r (read), w (write), and x (execute). Using chmod u+x *filename* will add execute permission for the owner of the file.

chown

The chown command changes the user and/or group that owns a file. It normally needs to be run as root using sudo e.g. sudo chown pi:root *filename* will change the owner to pi and the group to root.

ssh

ssh denotes the secure shell. Connect to another computer using an encrypted network connection. For more details see

scp

The scp command copies a file from one computer to another using ssh. For more details see

sudo

The sudo command enables you to run a command as a superuser, or another user. Use sudo -s for a superuser shell. For more details see

dd

The dd command copies a file converting the file as specified. It is often used to copy an entire disk to a single file or back again. So, for example, dd if=/dev/sdd of=backup.img will create a backup image from an SD card or USB disk drive at /dev/sdd. Make sure to use the correct drive when copying an image to the SD card as it can overwrite the entire disk.

df

Use df to display the disk space available and used on the mounted filesystems. Use df -h to see the output in a human-readable format using M for MBs rather than showing number of bytes.

unzip

The unzip command extracts the files from a compressed zip file.

tar

Use tar to store or extract files from a tape archive file. It can also reduce the space required by compressing the file similar to a zip file.

To create a compressed file, use tar -cvzf *filename.tar.gz* *directory/* To extract the contents of a file, use tar -xvzf *filename.tar.gz*

pipes

A pipe allows the output from one command to be used as the input for another command. The pipe symbol is a vertical line |. For example, to only show the first ten entries of the ls command it can be piped through the head command ls | head

tree

Use the tree command to show a directory and all subdirectories and files indented as a tree structure.

&

Run a command in the background with &, freeing up the shell for future commands.

wget

Download a file from the web directly to the computer with wget. So wget https://www.raspberrypi.org/documentation/linux/usage/commands.md will download this file to your computer as commands.md

curl

Use curl to download or upload a file to/from a server. By default, it will output the file contents of the file to the screen.

man

Show the manual page for a file with man. To find out more, run man man to view the manual page of the man command.

Search

grep

Use grep to search inside files for certain search patterns. For example, grep "search" *.txt will look in all the files in the current directory ending with .txt for the string search.

The grep command supports regular expressions which allows special letter combinations to be included in the search.

awk

awk is a programming language useful for searching and manipulating text files.

find

The find command searches a directory and subdirectories for files matching certain patterns.

whereis

Use whereis to find the location of a command. It looks through standard program locations until it finds the requested command.

Networking

ping

The ping utility is usually used to check if communication can be made with another host. It can be used with default settings by just specifying a hostname (e.g. ping raspberrypi.org) or an IP address (e.g. ping 8.8.8.8). It can specify the number of packets to send with the -c flag.

nmap

nmap is a network exploration and scanning tool. It can return port and OS information about a host or a range of hosts. Running just nmap will display the options available as well as example usage.

hostname

The hostname command displays the current hostname of the system. A privileged (super) user can set the hostname to a new one by supplying it as an argument (e.g. hostname new-host).

ifconfig

Use ifconfig to display the network configuration details for the interfaces on the current system when run without any arguments (i.e. ifconfig). By supplying the command with the name of an interface (e.g. eth0 or lo) you can then alter the configuration: check the manual page for more details.