How can I download all usernames?

Question

I have access to a university's Linux server where all students have accounts. I can retrieve their full name by typing the finger username, and their departments by typing id username. All the student usernames are consecutive. For example:

e205846
e205847
e205848
e205849
e205850
...

Is it possible for me to write a some kind of script and retrieve all the information to some kind of database? Or is there already an available tool for that? Also, as side note there some www folders in the Linux which has all the usernames.

Here is one example

e147290@beluga:~$ finger e204158
Login: e204158                          Name: april oneil
Directory: /home705/e204158             Shell: /bin/bash
Never logged in.
No mail.
No Plan.

e147290@beluga:~$ id e204159
uid=53653(e204158) gid=5621(ce_bs) groups=5621(ce_bs)

Answer 1

On Linux systems there's the getent program, which utilizes the standard get*ent(2) functions (getpwent() being the one to use here). What you want to retrieve are the contents of the passwd database (try man nsswitch.conf for a further understanding):

$ getent passwd
root:x:0:0:root:/root:/bin/bash
sashroot:x:0:0:root:/root:/bin/sash
daemon:x:1:1:daemon:/usr/sbin:/bin/sh
bin:x:2:2:bin:/bin:/bin/sh
sys:x:3:3:sys:/dev:/bin/sh
sync:x:65004:65534:sync:/bin:/bin/sync
games:x:65005:65060:games:/usr/games:/bin/sh
man:x:65006:65012:man:/var/cache/man:/bin/sh
lp:x:65007:7:lp:/var/spool/lpd:/bin/sh
mail:x:65008:65008:mail:/var/mail:/bin/sh
...

It gets a lot more interesting after the standard system accounts scrolled by.

If you're not an a Linux system, you can get this rather easy by writing something that dumps the user database on its own by using the getpwent(2) function. An example in C would be something like this:

#include <sys/types.h>
#include <pwd.h>
#include <stdio.h>

int
main(void)
{
    struct passwd *pwd;

    while ((pwd = getpwent()) != NULL) {
        printf("user = `%s', uid = %d, gid = %d, name = `%s'\n",
               pwd->pw_name, pwd->pw_uid, pwd->pw_gid, pwd->pw_gecos);
    }

    return 0;
}

Put this in a file test.c and build it with

$ gcc -o test test.c

Then you can call ./test and look what you get:

$ ./test
user = `root', uid = 0, gid = 0, name = `root'
user = `sashroot', uid = 0, gid = 0, name = `root'
user = `daemon', uid = 1, gid = 1, name = `daemon'
user = `bin', uid = 2, gid = 2, name = `bin'
user = `sys', uid = 3, gid = 3, name = `sys'
user = `sync', uid = 65004, gid = 65534, name = `sync'
user = `games', uid = 65005, gid = 65060, name = `games'
user = `man', uid = 65006, gid = 65012, name = `man'
user = `lp', uid = 65007, gid = 7, name = `lp'
user = `mail', uid = 65008, gid = 65008, name = `mail'
...

As above, it'll get more interesting later on.

The approach of using getwent() has the big advantage that you don't have to make any assumptions on how the login system is configured (/etc/passwd, LDAP, NIS, …?) but just let the system retrieve the information with its actual configuration.

Edit: It might happen that the passwd database's storage backend, e.g. LDAP, doesn't permit enumerating the database (and thus getpwent()) but only hand you out data sets explicitly requested by key (e.g. login name or UID, so getpwuid() or getpwnam() might work). In this case (and since your target user names are so neatly named) you could still "enumerate" manually with a modification of @masegaloeh's script:

#!/bin/bash

for i in {000000..999999}; do 
    getent passwd "e${i}" 2> /dev/null
done

How to do this in absence of getent with the system API (getpwnam(), getpwuid()) is left as an exercise to the reader.

Answer 2

getent is indeed the right way to access any database through the name switch on a Unix/Linux system, so it doesn't matter if accounts are stored locally in /etc/passwd, or if they are in LDAP, AD, NIS, or whatever service you have configured in nsswitch.conf.

So I'd do:

getent passwd | awk -F: '$1 ~"^e[0-9]*$" {print $5}'

This will print the full usernames for all accounts beginning with 'e' and followed by only digits.

If I needed to do this on a Windows system, I'd install cygwin and then do it as above :). In fact I just tested getent on Windows/cygwin and it works great (somewhat surprisingly).

Answer 3

This bash script will do looping for you

#!/bin/bash
for i in {205846..205850}; do
    finger e${i}
    id e${i}
done

You just modify 205846 and 205850 to get different range

Answer 4

/etc/password output is your safest bet as finger will print duplicates if some part of the name matches.

The following bash script should do the trick, it'll output user $output of id user

l=$(grep "^UID_MIN" /etc/login.defs)

# get max UID limit
#l1=$(grep "^UID_MAX" /etc/login.defs)

# if not set, set manually
l1=4999

# get all users and assign to users array
users=$(awk -F':' -v "min=${l##UID_MIN}" -v "max=${l1##UID_MAX}" '{ if ( $3 >= min && $3 <= max ) print $0}' /etc/passwd | awk 'BEGIN { FS = ":" } ; { print $1 }')

# print the needed info
for user in $users ; do echo -n $user && echo -n " " && id $user ; done

If you change the last line to

for user in $users ; do echo "INSERT INTO users(name,groups) VALUES('$user', '`id $user`');" ; done

It'll get you SQL insert statements, e.g

INSERT INTO users(name,groups) VALUES('priit', 'uid=1056(priit) gid=1056(priit) grupid=1056(priit)');

Answer 5

You can get all user information from /etc/passwd