Linux Essentials Skills Exam (IST-190)

Create three directories (reports, archive, scratch) in one command

mkdir reports archive scratch

Create five files log1 through log5 in one command using brace expansion

touch log{1..5}

Move log1 and log2 into the archive directory in one command

mv log1 log2 archive/

Copy log3 into scratch and rename the copy to backup3

cp log3 scratch/backup3

Create a hard link named reportlink pointing to reports/log4

ln reports/log4 reportlink

Create a symbolic link named scratchlink pointing to the scratch directory

ln -s scratch scratchlink

Save the first 3 lines of a file into a new file using redirection

head -3 file > newfile

Append the last 2 lines of a file to an existing file

tail -2 file >> existingfile

Vim command to copy the current line

yy

Vim command to paste a yanked or deleted line below the cursor

p

Vim command to delete the current line

dd

Vim command to save and quit

:wq

Vim command to quit without saving

:q!

Generate an SSH key pair with the default settings

ssh-keygen

Generate an SSH key pair with a custom file name

ssh-keygen -f ~/.ssh/keyname

Push your public key to a remote host for passwordless login

ssh-copy-id -i ~/.ssh/keyname.pub user@host

Run a single remote command over SSH using a specific private key, without opening a shell

ssh -i ~/.ssh/keyname user@host command

Start the SSH agent in your current shell

eval $(ssh-agent)

Load a passphrase-protected private key into the running SSH agent

ssh-add ~/.ssh/keyname

Create a new user named athos

useradd athos

Set or reset the password for user athos to redhat

passwd athos

Change a user's GECOS/comment field to "Operator One"

usermod -c "Operator One" username

Delete a user AND their home directory

userdel -r username

Create a group named musketeers with a specific GID of 22000

groupadd -g 22000 musketeers

Create a group and let the system assign the GID automatically

groupadd groupname

Add an existing user to a supplementary group WITHOUT removing their other groups

usermod -aG groupname username

Two-letter command to confirm a user's group memberships

id username

Which config file shows supplementary group membership for verification

/etc/group

Which config file shows a user's primary group and account info, not supplementary groups

/etc/passwd

Grant an entire group sudo access via sudoers.d

echo "%groupname ALL=(ALL) ALL" >> /etc/sudoers.d/groupname

Grant a single user sudo access via sudoers.d

echo "username ALL=(ALL) ALL" >> /etc/sudoers.d/username

Force a user to change their password at next login

chage -d 0 username

Set the minimum number of days before a password can be changed again

chage -m 10 username

Set the maximum number of days before a password expires

chage -M 30 username

Make umask 007 persistent for a user across logins

echo "umask 007" >> ~/.bashrc then source ~/.bashrc

Change only the group ownership of a file or directory

chown :groupname path (or chgrp groupname path)

Change both owner and group ownership at once

chown user:group path

Add write permission for the group owner using symbolic mode

chmod g+w path

Set permissions to rwxrwx--- using octal notation

chmod 770 path

Set the group's permissions to exactly rwx using symbolic mode

chmod g=rwx path

Set the sticky bit so only a file's owner can delete their own file in a shared directory

chmod o+t path

Set setgid on a directory so new files inherit the directory's group owner

chmod g+s path

Let others view and enter a directory but not modify its contents

chmod o+rx path

Let others cd into your home directory without being able to list its contents

chmod o+x path

Formula to calculate resulting file permissions from a umask value

666 minus the umask value (per digit)

Formula to calculate resulting directory permissions from a umask value

777 minus the umask value (per digit)

Resulting file/directory permissions for umask 022

Files 644, directories 755

Resulting file/directory permissions for umask 027

Files 640, directories 750

Command with no arguments to display your current default umask

umask

Temporarily set umask to 024 for the current shell session only

umask 024

Run a command in the background instead of the foreground

command &

List active and suspended background processes alongside their assigned ID numbers.

jobs

Suspend a running background job referenced by job number 1

kill -SIGSTOP %1

Resume a suspended background job referenced by job number 1

kill -SIGCONT %1

Gracefully ask a process to terminate (the default, catchable signal)

kill -SIGTERM %# (kill %#)

Force-kill a process that ignored SIGTERM

kill -SIGKILL %# (signal number 9)

Kill a process by name instead of by PID or job number

pkill -SIGTERM processname

Find the PID(s) of a running process by name

ps -ef | grep processname (or pgrep -a processname)

Confirm whether a specific PID is still running

ps -p PID

Inside top, which key quits the program

q

List all currently active/loaded service units

systemctl list-units --type=service

List all service unit files with their enabled/disabled state, including inactive ones

systemctl list-unit-files --type=service

Check the detailed current status of a specific service

systemctl status servicename

Check whether a service is set to start automatically at boot

systemctl is-enabled servicename

Check whether a service is currently running right now

systemctl is-active servicename

Start a stopped service immediately

systemctl start servicename

Stop a running service immediately

systemctl stop servicename

Stop and then start a service, changing its PID

systemctl restart servicename

Re-read a service's configuration WITHOUT changing its PID

systemctl reload servicename

Configure a service to start automatically at boot (without changing its current running state)

systemctl enable servicename

Configure a service to NOT start automatically at boot (without stopping it now)

systemctl disable servicename

Reboot the entire machine from the command line

systemctl reboot