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

For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))

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!
(written 2008-08-27, updated 2008-09-04)

Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles

A199 - Web Application Deployment - Additional Linux Administration
  [476] May I be politically incorrect? - (2005-10-25)
  [1292] DHCP automatic IP address v Static IP - (2007-08-06)
  [2232] Why sendmail one way, and pop3 the other? - (2009-06-12)

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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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