This is a general Linux question:

$ id db2inst1
uid=1512(db2inst1) gid=1505(db2iadm1) groups=1505(db2iadm1),1508(candle)

$ groups db2inst1
db2inst1 : db2iadm1 candle

$ more /etc/passwd | grep 1505
db2inst1:x:1512:1505::/xxx/db2/db2inst1:/bin/bash

$ more /etc/group | grep db2iadm1
db2iadm1:x:1505:


/etc/group doesn't list db2inst1 being part of db2iadm1. Does anyone know why it's this way on Lunux? Does it have to do with how the user/group was created or this is just a Linux thing?

Just found one Linux server (one out of many) where the primary group of a user in present in /etc/group.

Example:

~> more /etc/group | grep db2
db2iadm1:!:1008:
db2fadm1:!:1007:db2fenc1


~> id db2inst1; id db2fenc1
uid=2006(db2inst1) gid=1008(db2iadm1) groups=1001(candle),1008(db2iadm1)
uid=2007(db2fenc1) gid=1007(db2fadm1) groups=1007(db2fadm1)



Another server shows:

~> more /etc/group | grep db2
db2iadm1:!:1008:
db2fadm1:!:1007:


~> id db2inst1; id db2fenc1
uid=1502(db2inst1) gid=1008(db2iadm1) groups=1001(candle),1008(db2iadm1)
uid=1503(db2fenc1) gid=1007(db2fadm1) groups=1007(db2fadm1)



Both servers are zLinux:

/etc/SuSE-release:
SUSE Linux Enterprise Server 10 (s390x)
VERSION = 10
PATCHLEVEL = 4


Anyone knows why?

I'd be suspect of the machine that is different if it is the only one.
The two machines I checked, both SuSE 11.2, showed as you would expect.

I've done some reading since posting my question. Based on my understanding, on Linux: the primary group info is stored in /etc/passwd and the secondary group info in /etc/group. So, I should only see my secondary groups listed in /etc/group. But what I'm not sure about is why some user's primary group appear in /etc/group and some don't.

Example:

$ id vjxxxx
uid=1511(vjxxxx) gid=1509(staff) groups=1509(staff),1510(sysgrp)

$ id bkxxxx
uid=1507(bkxxxx) gid=1509(staff) groups=1509(staff),1510(sysgrp)

$ more /etc/group | grep staff
staff:x:1509:bkxxxx


The primary group of vjxxxx and bkxxxx is staff; however, /etc/group contains bkxxxx but not vjxxxx.



If I create a new user on this server (RHEL 5.8) , I don't see it in /etc/group:


# groupadd -g 777 db2g

# more /etc/group | grep db2g
db2g:x:777:

# useradd -g db2g db2u

# id db2u
uid=1513(db2u) gid=777(db2g) groups=777(db2g)

# more /etc/group | grep db2g
db2g:x:777:


Oh, well... I just have to remember that Linux is different from AIX when it comes to /etc/group.

Looking at the Red Hat Linux, I suspect that the primary group membership does not show in /etc/groups. Only if you explicitly do "usermod -G db2g db2u", setting db2g as a supplementary group, will db2u show in /etc/group for db2g.

I don't have an AIX box to check if it's different there.

Bingo! Thank you.