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Diffstat (limited to 'man/systemd-nspawn.xml')
| -rw-r--r-- | man/systemd-nspawn.xml | 99 |
1 files changed, 69 insertions, 30 deletions
diff --git a/man/systemd-nspawn.xml b/man/systemd-nspawn.xml index a0376ed3e0..ea0c6562f8 100644 --- a/man/systemd-nspawn.xml +++ b/man/systemd-nspawn.xml @@ -387,38 +387,77 @@ <varlistentry> <term><option>--private-users=</option></term> - <listitem><para>Enables user namespacing. If enabled, the - container will run with its own private set of Unix user and - group ids (UIDs and GIDs). Takes none, one or two - colon-separated parameters: the first parameter specifies the - first host UID to assign to the container, the second - parameter specifies the number of host UIDs to assign to the - container. If the second parameter is omitted, 65536 UIDs are - assigned. If the first parameter is also omitted (and hence - no parameter passed at all), the first UID assigned to the - container is read from the owner of the root directory of the - container's directory tree. By default, no user namespacing is - applied.</para> - - <para>Note that user namespacing currently requires OS trees - that are prepared for the UID shift that is being applied: - UIDs and GIDs used for file ownership or in file ACL entries - must be shifted to the container UID base that is - used during container runtime.</para> - - <para>It is recommended to assign at least 65536 UIDs to each - container, so that the usable UID range in the container - covers 16 bit. For best security, do not assign overlapping UID - ranges to multiple containers. It is hence a good idea to use - the upper 16 bit of the host 32-bit UIDs as container - identifier, while the lower 16 bit encode the container UID - used.</para> - - <para>When user namespaces are used, the GID range assigned to - each container is always chosen identical to the UID - range.</para></listitem> + <listitem><para>Controls user namespacing. If enabled, the container will run with its own private set of UNIX + user and group ids (UIDs and GIDs). This involves mapping the private UIDs/GIDs used in the container (starting + with the container's root user 0 and up) to a range of UIDs/GIDs on the host that are not used for other + purposes (usually in the range beyond the host's UID/GID 65536). The parameter may be specified as follows:</para> + + <orderedlist> + <listitem><para>The value <literal>no</literal> turns off user namespacing. This is the default.</para></listitem> + + <listitem><para>The value <literal>yes</literal> (or the omission of a parameter) turns on user + namespacing. The UID/GID range to use is determined automatically from the file ownership of the root + directory of the container's directory tree. To use this option, make sure to prepare the directory tree in + advance, and ensure that all files and directories in it are owned by UIDs/GIDs in the range you'd like to + use. Also, make sure that used file ACLs exclusively reference UIDs/GIDs in the appropriate range. If this + mode is used the number of UIDs/GIDs assigned to the container for use is 65536, and the UID/GID of the + root directory must be a multiple of 65536.</para></listitem> + + <listitem><para>The value "pick" turns on user namespacing. In this case the UID/GID range is automatically + chosen. As first step, the file owner of the root directory of the container's directory tree is read, and it + is checked that it is currently not used by the system otherwise (in particular, that no other container is + using it). If this check is successful, the UID/GID range determined this way is used, similar to the + behaviour if "yes" is specified. If the check is not successful (and thus the UID/GID range indicated in the + root directory's file owner is already used elsewhere) a new – currently unused – UID/GID range of 65536 + UIDs/GIDs is randomly chosen between the host UID/GIDs of 524288 and 1878982656, always starting at a + multiple of 65536. This setting implies <option>--private-users-chown</option> (see below), which has the + effect that the files and directories in the container's directory tree will be owned by the appropriate + users of the range picked. Using this option makes user namespace behaviour fully automatic. Note that the + first invocation of a previously unused container image might result in picking a new UID/GID range for it, + and thus in the (possibly expensive) file ownership adjustment operation. However, subsequent invocations of + the container will be cheap (unless of course the picked UID/GID range is assigned to a different use by + then).</para></listitem> + + <listitem><para>Finally if one or two colon-separated numeric parameters are specified, user namespacing is + turned on, too. The first parameter specifies the first host UID/GID to assign to the container, the second + parameter specifies the number of host UIDs/GIDs to assign to the container. If the second parameter is + omitted, 65536 UIDs/GIDs are assigned.</para></listitem> + </orderedlist> + + <para>It is recommended to assign at least 65536 UIDs/GIDs to each container, so that the usable UID/GID range in the + container covers 16 bit. For best security, do not assign overlapping UID/GID ranges to multiple containers. It is + hence a good idea to use the upper 16 bit of the host 32-bit UIDs/GIDs as container identifier, while the lower 16 + bit encode the container UID/GID used. This is in fact the behaviour enforced by the + <option>--private-users=pick</option> option.</para> + + <para>When user namespaces are used, the GID range assigned to each container is always chosen identical to the + UID range.</para> + + <para>In most cases, using <option>--private-users=pick</option> is the recommended option as it enhances + container security massively and operates fully automatically in most cases.</para> + + <para>Note that the picked UID/GID range is not written to <filename>/etc/passwd</filename> or + <filename>/etc/group</filename>. In fact, the allocation of the range is not stored persistently anywhere, + except in the file ownership of the files and directories of the container.</para></listitem> </varlistentry> + <varlistentry> + <term><option>-U</option></term> + + <listitem><para>Equivalent to <option>--private-users=pick</option>.</para></listitem> + </varlistentry> + + <varlistentry> + <term><option>--private-users-chown</option></term> + + <listitem><para>If specified, all files and directories in the container's directory tree will adjusted so that + they are owned to the appropriate UIDs/GIDs selected for the container (see above). This operation is + potentially expensive, as it involves descending and iterating through the full directory tree of the + container. Besides actual file ownership, file ACLs are adjusted as well.</para> + + <para>This option is implied if <option>--private-users=pick</option> is used. This option has no effect if + user namespacing is not used.</para></listitem> + </varlistentry> <varlistentry> <term><option>--private-network</option></term> |