Let’s get some entries with ‘getent’, e.g. passwd or group.
sudo adduser maestro
add user ‘maestro’
This depends upon the settings in the /etc/default/useradd file and /etc/login.defs
sudo useradd -m pinkie
add user ‘pinkie’ with a home directory
sudo adduser -m -e 2017-04-25 temp
add expiry date to user
userdel -r maestro
delete maestro and hir homefolder
find which group you are in
id -Gn maestro
Find which groups maestro is in
deluser –remove-home maestro
delete user maestro
usermod -aG sudo maestro
add user maestro to group sudo
list users’ passwords (and therefore users)
create the group ‘awesome’
passwords are stored in /etc/shadow.
there are user accounts for processes such as ‘bin’ and ’nobody’ which are locked, so they’re unusable.
passwd -l bin
lock the user ‘bin’
more /etc/passwd | grep games
we find the name, password and user id of the user ‘games’. I.e. the password is ‘x’, and the user id is ‘5’. The password is an impossible hash, so no input password could match.
groupdel learners | delete the group ’learners’
gpasswd -d pi games | remove user ‘pi’ from the group ‘games’
find the id number of group ‘games’ (60)
usermod -aG sudo maestro
add user to group ‘maestro’
user info is stored in /etc’s passwd, shadow, group and gshadow
The default new user profiles are under /etc/skel.
A list of shells is in /etc/shells.
Only root can run shells not listed in /etc/shells
To change a user’s shell:
usermod –shell /bin/bash user1
Alternatively, change the shell in /etc/passwd.
Usermod also lets you change a user’s username:
usermod -l henry mark
However, this will not change the home directory.
Lock a user out of an account:
usermod -L henry
-G or -groups adds the user to other groups:
usermod -G sudo henry
-s adds the user to a shell.
-u let’s you manually specifiy a UID.
In /etc/group, a group file may look like this:
We can use groupmod, like like usermod, e.g. to change a name:
groupmod -n frontoffice backoffice
Delte a group:
See list of logged on users.
See last logons:
or all logon attempts, including bad attempts:
List recently accessed files:
See files opened by steve
lsof -t -u steve
See files opened by anyone but steve
lsof -u ^steve
Fuser can also track people loggingin:
… and fuser can kill everything accessing the home directory:
fuser -km /home
Looking for Dodgy Files
Some files can be executed by people as if they had super user permissions, and that’s okay… sometimes.
Let’s start with files executable by user:
sudo find / -type f -perm -g=s -ls
And then those executable by the group:
find / -type f -perm -g=s -ls
And finally, worrying files, executable by anyone as if sie were the owner:
find / -xdev ( -o -nogroup ) -print
Then have a look at resource usage per user.
sudo chmod u+s process.sh
This will modify process.sh to that instead of being simply executable, anyone executing it will have the permissions as if owner while executing it.