About System Users and Groups

Throughout BLFS, many packages install programs that run as daemons or in some way should have a user or group name assigned. Generally these names are used to map a user ID (uid) or group ID (gid) for system use. Generally the specific uid or gid numbers used by these applications are not significant. The exception of course, is that root has a uid and gid of 0 (zero) that is indeed special. The uid values are stored in /etc/passwd and the gid values are found in /etc/group.

Customarily, Unix systems classify users and groups into two categories: system users and regular users. The system users and groups are given low numbers and regular users and groups have numeric values greater than all the system values. The cutoff for these numbers is found in two parameters in the /etc/login.defs configuration file. The default UID_MIN value is 1000 and the default GID_MIN value is 1000. If a specific uid or gid value is not specified when creating a user with useradd or a group with groupadd the values assigned will always be above these cutoff values.

Additionally, the Linux Standard Base recommends that system uid and gid values should be below 100.

Below is a table of suggested uid/gid values used in BLFS beyond those defined in a base LFS installation. These can be changed as desired, but provide a suggested set of consistent values.

Table 3.1. UID/GID Suggested Values

Name uid gid
bin 1
lp 9
adm 16
atd 17 17
messagebus 18 18
lpadmin   19
named 20 20
gdm 21 21
fcron 22 22
systemd-journal   23
apache 25 25
smmsp 26 26
polkitd 27 27
exim 31 31
postfix 32 32
postdrop 33
sendmail 34
mail 34
vmailman 35 35
news 36 36
kdm 37 37
mysql 40 40
postgres 41 41
dovecot 42 42
dovenull 43 43
ftp 45 45
proftpd 46 46
vsftpd 47 47
rsyncd 48 48
sshd 50 50
stunnel 51 51
svn 56 56
svntest 57
games 60 60
kvm 61
wireshark 62
lightdm 63 63
systemd-bus-proxy 64 64
systemd-journal-gateway 65 65
systemd-network 66 66
systemd-resolve 67 67
systemd-timesync 68 68
scanner 70
colord 71 71
ldap 83 83
avahi 84 84
avahi-autoipd 85 85
netdev 86
ntp 87 87
unbound 88 88
anonymous 98
nobody 99
nogroup 99

One value that is missing is 65534. This value is customarily assigned to the user nobody and group nogroup and is unnecessary.

Last updated on 2014-06-12 12:31:05 +0000