UNIX Users & Groups

getent is the preferred way of retrieving this information (on Linux) as your system may be using additional (or alternative) NSS 'databases' (like LDAP)

User

cat /etc/passwd

getent passwd

getent is the preferred way of retrieving this information (on Linux) as your system may be using additional (or alternative) NSS 'databases' (like LDAP)

Information on a single user...

getent passwd username

id username

finger -l username

To install finger on Linux...sudo apt install finger

Create

Group

groupadd groupname

MySQL Example

groupadd -g 27 -o -r mysql

The -g (or --gid) option specifies the group id (GID)The -o (or --non-unique) option permits to add a group with a non-unique GIDThe -r (or --system) option creates a system groupIn this example "mysql" is the group name

User

Usernames & Passwords

useradd -G groupname -d /home/username -m -s /bin/bash username

Defaults

Defaults are controlled by entries in...

/etc/default/useradd

/etc/login.defs

MySQL Example

useradd -M -N -g mysql -o -r -d /mysql/data -s /bin/false -c "MySQL Server" -u 27 mysql

The -M (--no-create-home) prevents creation of a home directory for the user.The -N (--no-user-group) prevents creation of a group with the same name as the user. The -g (--gid) specifies the group name or number of the user''s initial login group (mysql).The -o (--non-unique) permits to add a user with a duplicate/non-unique UID (-u option must also be supplied).The -r (--system) creates a system account (note that this means the -M above is actually redundant).The -d (--home-dir) specifies the user's login directory (/mysql/data). The Directory does not need to exist, but will not be created if missing.The -s (--shell) specifies the user's login shell. A value of /bin/false effectively prevents the user from being able to login.The -c (--comment) allows you to provide a short description for the login.The -u (--uid) specifies the user id (UID).In this example "mysql" is the username.For other available options see the man page.

Oracle Example

/usr/sbin/useradd -u 54321 -g oinstall -G dba,oper,asmdba,backupdba,dgdba,kmdba,racdba oracle

/usr/sbin/useradd -u 54331 -g oinstall -G dba,oper,asmdba,backupdba,dgdba,kmdba,racdba grid

Passwords

Change

passwd username

Generate

Usernames & Passwords

There are several ways to generate a secure password from the UNIX command prompt. Alterntively use a password manager or website to generate a secure password and paste it in.

openssl rand -base64 32

dd if=/dev/urandom bs=1 count=32 2>/dev/null | base64 -w 0 | rev | cut -b 2- | rev

tr -cd '[:alnum:]' < /dev/urandom | fold -w30 | head -n1

date +%s | sha256sum | base64 | head -c 32 ; echo

date | md5sum

Delete

Group

groupdel groupname

User

At its simplest...

userdel username

Other scenarios...

userdel --remove --selinux-user username

Removes home directory and all files in it,and removes any SELinux mappings

SELinux

Modify

Add User to Group

To add an additional secondary group to a user...

usermod -a -G newgroup myuser

The -a [--append] appends to existing list of group membershipsThe -G [--groups] specifies the group membership to add

Alternatively...

adduser myuser newgroup

To make the group the primary group for the current session without logging out and logging back in...

newgrp oper

To add the group to the list of secondary groups for the current session without logging out and logging back in...

sg oracle oper

Remove User from Group

deluser myuser mygroup

Bibliography

https://stackoverflow.com/questions/17321224/creating-another-user-account-having-power-of-roothttps://www.howtogeek.com/howto/30184/10-ways-to-generate-a-random-password-from-the-command-line/https://man7.org/linux/man-pages/man1/getent.1.html
Usershttps://askubuntu.com/questions/79565/how-to-add-existing-user-to-an-existing-group
Groupshttps://linuxize.com/post/how-to-list-groups-in-linux/https://www.howtogeek.com/50787/add-a-user-to-a-group-or-second-group-on-linux/
fingerhttps://www.tutorialspoint.com/unix_commands/finger.htm
MySQL
https://stackoverflow.com/questions/36047558/cant-login-to-unix-mysql-user

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