What is my real and my effective ID? [Linux]

Archive - Originally posted on "The Horse's Mouth" - 2008-08-27 18:01:00 - Graham Ellis
When you're logged in to a Linux or Unix system, you should normally be running through a user account - and not as the system administrator (root). The root account should be reserved for systems admin tasks where the extra authority is needed.

The who, users, whoami and id commands all tell you who you are running as ...

[trainee@crocus ~]$ who

trainee  pts/0        Aug 25 15:39 (192.168.200.90)

[trainee@crocus ~]$ who am i

trainee  pts/0        Aug 25 15:39 (192.168.200.90)

[trainee@crocus ~]$ users

trainee

[trainee@crocus ~]$ id -a

uid=500(trainee) gid=48(apache) groups=48(apache) 

context=user_u:system_r:unconfined_t

[trainee@crocus ~]$ whoami

trainee

[trainee@crocus ~]$

If you need root access, you should gain it using the su command with the - option - and that changes your effective user id to root, but leaves your real id as your original user.

The who and the users command will report your real id.
The id -a and the whoami command will report your effective id.

[trainee@crocus ~]$ su -

Password: ********

[root@crocus ~]# who

trainee  pts/0        Aug 25 15:39 (192.168.200.90)

[root@crocus ~]# who am i

trainee  pts/0        Aug 25 15:39 (192.168.200.90)

[root@crocus ~]# users

trainee

[root@crocus ~]# id -a

uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),

4(adm),6(disk),10(wheel) context=root:system_r:unconfined_t

[root@crocus ~]# whoami

root

[root@crocus ~]#

[b]Remember[/b] to exit as soon as you have done your root-y stuff from the root account!

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What is my real and my effective ID? [Linux]