Ubuntu Manpage: sysusers.d - Declarative allocation of system users and groups

NAME

       sysusers.d - Declarative allocation of system users and groups

SYNOPSIS

       /etc/sysusers.d/*.conf

       /run/sysusers.d/*.conf

       /usr/lib/sysusers.d/*.conf

DESCRIPTION

       systemd-sysusers uses the files from sysusers.d directory to create system users and
       groups and to add users to groups, at package installation or boot time. This tool may be
       used to allocate system users and groups only, it is not useful for creating non-system
       (i.e. regular, "human") users and groups, as it accesses /etc/passwd and /etc/group
       directly, bypassing any more complex user databases, for example any database involving
       NIS or LDAP.

CONFIGURATION DIRECTORIES AND PRECEDENCE

       Each configuration file shall be named in the style of package.conf or package-part.conf.
       The second variant should be used when it is desirable to make it easy to override just
       this part of configuration.

       Files in /etc/sysusers.d override files with the same name in /usr/lib/sysusers.d and
       /run/sysusers.d. Files in /run/sysusers.d override files with the same name in
       /usr/lib/sysusers.d. Packages should install their configuration files in
       /usr/lib/sysusers.d. Files in /etc/sysusers.d are reserved for the local administrator,
       who may use this logic to override the configuration files installed by vendor packages.
       All configuration files are sorted by their filename in lexicographic order, regardless of
       which of the directories they reside in. If multiple files specify the same path, the
       entry in the file with the lexicographically earliest name will be applied. All later
       entries for the same user and group names will be logged as warnings.

       If the administrator wants to disable a configuration file supplied by the vendor, the
       recommended way is to place a symlink to /dev/null in /etc/sysusers.d/ bearing the same
       filename.

CONFIGURATION FILE FORMAT

The file format is one line per user or group containing name, ID, GECOS field
description, home directory, and login shell:

#Type Name ID GECOS Home directory Shell
u httpd 404 "HTTP User"
u authd /usr/bin/authd "Authorization user"
u postgres - "Postgresql Database" /var/lib/pgsql /usr/libexec/postgresdb
g input - -
m authd input
u root 0 "Superuser" /root /bin/zsh

Empty lines and lines beginning with the "#" character are ignored, and may be used for
commenting.

Type
The type consists of a single letter. The following line types are understood:

u
Create a system user and group of the specified name should they not exist yet. The
user's primary group will be set to the group bearing the same name. The account will
be created disabled, so that logins are not allowed.

g
Create a system group of the specified name should it not exist yet. Note that u
implicitly create a matching group. The group will be created with no password set.

m
Add a user to a group. If the user or group do not exist yet, they will be implicitly
created.

r
Add a range of numeric UIDs/GIDs to the pool to allocate new UIDs and GIDs from. If no
line of this type is specified, the range of UIDs/GIDs is set to some compiled-in
default. Note that both UIDs and GIDs are allocated from the same pool, in order to
ensure that users and groups of the same name are likely to carry the same numeric UID
and GID.

Name
The name field specifies the user or group name. The specified name must consist only of
the characters a-z, A-Z, 0-9, "_" and "-", except for the first character which must be
one of a-z, A-Z or "_" (i.e. numbers and "-" are not permitted as first character). The
user/group name must have at least one character, and at most 31.

It is strongly recommended to pick user and group names that are unlikely to clash with
normal users created by the administrator. A good scheme to guarantee this is by prefixing
all system and group names with the underscore, and avoiding too generic names.

For m lines, this field should contain the user name to add to a group.

For lines of type r, this field should be set to "-".

ID
For u and g, the numeric 32-bit UID or GID of the user/group. Do not use IDs 65535 or
4294967295, as they have special placeholder meanings. Specify "-" for automatic UID/GID
allocation for the user or group (this is strongly recommended unless it is strictly
necessary to use a specific UID or GID). Alternatively, specify an absolute path in the
file system. In this case, the UID/GID is read from the path's owner/group. This is useful
to create users whose UID/GID match the owners of pre-existing files (such as SUID or SGID
binaries). The syntax "uid:gid" is also supported to allow creating user and group pairs
with different numeric UID and GID values. The group with the indicated GID must get
created explicitly before or it must already exist. Specifying "-" for the UID in this
syntax is also supported.

For m lines, this field should contain the group name to add to a user to.

For lines of type r, this field should be set to a UID/GID range in the format "FROM-TO",
where both values are formatted as decimal ASCII numbers. Alternatively, a single UID/GID
may be specified formatted as decimal ASCII numbers.

GECOS
A short, descriptive string for users to be created, enclosed in quotation marks. Note
that this field may not contain colons.

Only applies to lines of type u and should otherwise be left unset (or "-").

Home Directory
The home directory for a new system user. If omitted, defaults to the root directory.

Only applies to lines of type u and should otherwise be left unset (or "-"). It is
recommended to omit this, unless software strictly requires a home directory to be set.

Shell
The login shell of the user. If not specified, this will be set to /sbin/nologin, except
if the UID of the user is 0, in which case /bin/sh will be used.

Only applies to lines of type u and should otherwise be left unset (or "-"). It is
recommended to omit this, unless a shell different /sbin/nologin must be used.

IDEMPOTENCE