1) From "/etc/passwd - Using Cut & Awk Command
A file called "/etc/passwd" stores all users list regardless of created account for a human, service associated account or system functional user. Each line of "/etc/passwd" is a distinct user. These commands should work on Centos/Ubuntu/Arch and other linux distros as well.
Use below command to list all user
$ cat /etc/passwd
root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:/sbin/nologin daemon:x:2:2:daemon:/sbin:/sbin/nologin adm:x:3:4:adm:/var/adm:/sbin/nologin lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin nobody:x:99:99:Nobody:/:/sbin/nologin dbus:x:81:81:System message bus:/:/sbin/nologin polkitd:x:999:998:User for polkitd:/:/sbin/nologin hacluster:x:189:189:cluster user:/home/hacluster:/sbin/nologin avahi-autoipd:x:170:170:Avahi IPv4LL Stack:/var/lib/avahi-autoipd:/sbin/nologin rpc:x:32:32:Rpcbind Daemon:/var/lib/rpcbind:/sbin/nologin rpcuser:x:29:29:RPC Service User:/var/lib/nfs:/sbin/nologin nfsnobody:x:65534:65534:Anonymous NFS User:/var/lib/nfs:/sbin/nologin ...
you get list without un-necessary information by using,
$ cut -d : -f 1 /etc/passwd
The cut is a command for formatting each line of files and display only required output on the console. Basically, the cut command cuts a line and extracts the text. Remember, cut command needs option otherwise it gives error.
root daemon bin sys sync games man lp mail news uucp proxy www-data backup ....
Let's try something more,
$ cat /etc/passwd | grep "/home" |cut -d: -f1
syslog administrator ucartz ...
Now what we have done is, we have piped the previous command output to another variable "cut"
$ cut -d: -f1
-d defines delimiter ":"
-f1 display first field of line i.e. username.
Let us try some more formatting, Awk is a utility that enables a system administrator to build commands that define text patterns that need to be searched in a file. Awk is mostly used for post-processing & Pattern Matching.Now let us try some formatting the output, the below prints more than just the login names. awk command print out the full name and home directory along with the login,
$ awk -F":" '{print "Login:" $1 "\tName:" $5 "\tHome:" $6}' /etc/passwd
look at the output, you will see well formatted and decorated output as compared to nay other command,
Login:root Name:root Home:/root Login:daemon Name:daemon Home:/usr/sbin Login:bin Name:bin Home:/bin Login:sys Name:sys Home:/dev Login:sync Name:sync Home:/bin Login:games Name:games Home:/usr/games Login:man Name:man Home:/var/cache/man Login:lp Name:lp Home:/var/spool/lpd Login:mail Name:mail Home:/var/mail Login:gnats Name:Gnats Bug-Reporting System (admin) Home:/var/lib/gnats ...
2) Getent command
The getent command do the same like cut command we have seen before, getent command fetches entries from databases supported by the Name Service library. If one or more options are provided to command, then only the entries that match the option will be displayed. Otherwise, all entries will be displayed. the syntax for getting end command,
getent [option] [database]
Display all Users
This is same as that of listing users using cat /etc/passwd, if no other options are provided the getent command uses passwd as database reference and lists all users.
$ getent passed
root:x:0:0:root:/root:/bin/bash bin:x:1:1:bin:/bin:/sbin/nologin daemon:x:2:2:daemon:/sbin:/sbin/nologin adm:x:3:4:adm:/var/adm:/sbin/nologin saslauth:x:996:76:"Saslauthd user":/run/saslauthd:/sbin/nologin libstoragemgmt:x:995:994:daemon account for libstoragemgmt:/var/run/lsm:/sbin/nologin avahi:x:70:70:Avahi mDNS/DNS-SD Stack:/var/run/avahi-daemon:/sbin/nologin ntp:x:38:38::/etc/ntp:/sbin/nologin mysql:x:27:27:MariaDB Server:/var/lib/mysql:/sbin/nologin radvd:x:75:75:radvd user:/:/sbin/nologin vivek:x:1000:1000:vivek:/home/vivek:/bin/bash vboxadd:x:991:1::/var/run/vboxadd:/bin/false ucartz:x:9999:9999:official:/home/lino_dir:/bin/bash ...
Find all Groups
The below commands list all group without any condition or matches if no other options are provided the getent command uses group as database reference and lists all groups.
$ getent group
root:x:0: bin:x:1: daemon:x:2: sys:x:3: adm:x:4: tty:x:5: disk:x:6: mail:x:12:postfix man:x:15: dialout:x:18: floppy:x:19: haclient:x:189: unbound:x:997: colord:x:996: dip:x:40: usbmuxd:x:113: ...
Search All groups with specific user
$ getent group | grep username
The above command fetches all group, passing username to pipe lists only matching row. The output has a group and username belonging to that group.
The below command is for advanced formatting using awk, cut & sed command together to list all users and users belongs to specific group.
cat /etc/group | awk -F: '{print $1, $3, $4}' | while read group gid members; do members=$members,$(awk -F: "\$4 == $gid {print \",\" \$1}" /etc/passwd);
echo "$group: $members" | sed 's/,,*/ /g';done
