Useful Linux

Useful Linux Commands!

Use with care

sudo -s

Important info

ethtool -P eth0    //MAC address (Permanent address)
hostname
hostname -I

uname -m           //Kernel information
uname -s
uname -r

cat /etc/os-release

Managing users

useradd <user>
passwd <user>
userdel <user>     //Only deletes users account
userdel -r <user>  //Removes user, home folder, and their files

getent group wheel
usermod -aG wheel <user>
su - <user>        //Switch users

Directories

rm -r -f <directory>           //Removes all files from directory
cp -a /source/. /dest/         //-a preserves all file attribures and symlinks
                               //. at the end allows to copy all files and folders including hidden ones
chown -R username:groupname *    Ex: chown -R jenkins:users *    //changes all ownership in file

cd -                           //Changes directory to previous working directory

List Stuff

ls -d */                       //List directories in a directory

Adding to Path

echo $PATH
PATH=$PATH:<Directory path>
export PATH

export PATH=$PATH:<Directory path>                     //All in one command    

echo 'PATH=$PATH:/opt/openmpi/bin' >> /etc/bashrc      //Another way to add path

Symlinks

ln -s /full/path/to/file /full/path/to/link/area

Ex:    ln -s /home/dylan/aws-pmix/mysqlauth.sh /home/dylan/aws-pmix/backend/shared/mysqlauth.sh

ls -Al    //In directory you created symlink. Should look something like this:
lrwxrwxrwx 1 dylan users   47 Jun 12 12:02 mysqlauth.sh -> /home/dylan/aws-pmix-scale-testing/mysqlauth.sh

The arrow pointing to the file path is the symlink. To delete a symlink, go into the directory with the symlink and:

rm fileName
Ex:  rm mysqlauth.sh

Figure out what stuff is

type <command>                //Tells you what type of command it is    
file <filename>               //Tells you what type of file it is
printenv | less               //Prints environment variables

Date

date
time

https://stackoverflow.com/questions/21721875/store-date-variable-in-bash-script

Less Command

Page Up or b         Scroll back one page
Page Down or space   Scroll forward one page
Up Arrow             Scroll up one line
Down Arrow           Scroll down one line
G                    Move to the end of the text file
1G or g              Move to the beginning of the text file
/_characters_        Search forward to the next occurrence of _characters_
?_characters_        Search backward to the next occurrence of _characters_
n                    Search for the next occurrence of the previous search
h                    Display help screen
q                    Quit less

Directories in Linux

Under "3-Exploring The System" in The Linux Command Line book

/            The root directory. Where everything begins.
/bin         Contains binaries (programs) that be must present for the system to boot and run
/boot      
/dev         This is a special directory which contains device nodes. “Everything is a file” also applies to devices. Here is where the kernel maintains a list of all the devices it understands.

/etc
/home
/lib          Contains shared library files used by the core system programs. These are similar to DLLs in Windows.
/lost+found
/media
/mnt
/opt
/proc
/root
/sbin
/tmp
/usr
/usr/bin
/usr/lib
/usr/local
/usr/sbin
/usr/share
/usr/share/doc
/var
/var/log