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-rw-r--r--man/systemd.exec.xml36
1 files changed, 32 insertions, 4 deletions
diff --git a/man/systemd.exec.xml b/man/systemd.exec.xml
index 49fea98a95..bfb4101d99 100644
--- a/man/systemd.exec.xml
+++ b/man/systemd.exec.xml
@@ -143,10 +143,38 @@
<term><varname>User=</varname></term>
<term><varname>Group=</varname></term>
- <listitem><para>Sets the Unix user or group that the processes
- are executed as, respectively. Takes a single user or group
- name or ID as argument. If no group is set, the default group
- of the user is chosen. These do not affect commands prefixed with <literal>!</literal>.</para></listitem>
+ <listitem><para>Set the UNIX user or group that the processes are executed as, respectively. Takes a single
+ user or group name, or numeric ID as argument. If no group is set, the default group of the user is used. This
+ setting does not affect commands whose command line is prefixed with <literal>!</literal>.</para></listitem>
+ </varlistentry>
+
+ <varlistentry>
+ <term><varname>DynamicUser=</varname></term>
+
+ <listitem><para>Takes a boolean parameter. If set, a UNIX user and group pair is allocated dynamically when the
+ unit is started, and released as soon as it is stopped. The user and group will not be added to
+ <filename>/etc/passwd</filename> or <filename>/etc/group</filename>, but are managed transiently during
+ runtime. The <citerefentry><refentrytitle>nss-systemd</refentrytitle><manvolnum>8</manvolnum></citerefentry>
+ glibc NSS module provides integration of these dynamic users/groups into the system's user and group
+ databases. The user and group name to use may be configured via <varname>User=</varname> and
+ <varname>Group=</varname> (see above). If these options are not used and dynamic user/group allocation is
+ enabled for a unit, the name of the dynamic user/group is implicitly derived from the unit name. If the unit
+ name without the type suffix qualifies as valid user name it is used directly, otherwise a name incorporating a
+ hash of it is used. If a statically allocated user or group of the configured name already exists, it is used
+ and no dynamic user/group is allocated. Dynamic users/groups are allocated from the UID/GID range
+ 61184…65519. It is recommended to avoid this range for regular system or login users. At any point in time
+ each UID/GID from this range is only assigned to zero or one dynamically allocated users/groups in
+ use. However, UID/GIDs are recycled after a unit is terminated. Care should be taken that any processes running
+ as part of a unit for which dynamic users/groups are enabled do not leave files or directories owned by these
+ users/groups around, as a different unit might get the same UID/GID assigned later on, and thus gain access to
+ these files or directories. If <varname>DynamicUser=</varname> is enabled, <varname>PrivateTmp=</varname> is
+ implied. This ensures that the lifetime of temporary files created by the executed processes is bound to the
+ runtime of the service, and hence the lifetime of the dynamic user/group. Since <filename>/tmp</filename> and
+ <filename>/var/tmp</filename> are usually the only world-writable directories on a system this ensures that a
+ unit making use of dynamic user/group allocation cannot leave files around after unit termination. Use
+ <varname>RuntimeDirectory=</varname> (see below) in order to assign a writable runtime directory to a service,
+ owned by the dynamic user/group and removed automatically when the unit is terminated. Defaults to
+ off.</para></listitem>
</varlistentry>
<varlistentry>