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Diffstat (limited to 'README.rst')
| -rw-r--r-- | README.rst | 23 |
1 files changed, 22 insertions, 1 deletions
@@ -8,6 +8,8 @@ Features -------- - minimal requirements (sh, mount, getopt) +- single shell script, no compilation required +- small (7 KB, 2 KB after gzip -9) Benefits over manually calling ``mkdir /tmp/x; mount ...`` @@ -26,10 +28,12 @@ mount point, it continues to access the original directory, not the overlaid one. Each process also has a cached root directory pointer, which can only be modified by chroot (internally) or pivot_root (globally). The pivot_root(2)_ and pivot_root(8)_ man pages should be fully read and understood before using -tmpoverlay to overmount ``/``. +tmpoverlay to overmount ``/``. It is also highly recommended to read `busybox +switch_root comment`_. .. _pivot_root(2): https://man7.org/linux/man-pages/man2/pivot_root.2.html .. _pivot_root(8): https://man7.org/linux/man-pages/man8/pivot_root.8.html +.. _busybox switch_root comment: https://git.busybox.net/busybox/tree/util-linux/switch_root.c?id=3b267e99259191eca0865179a56429c4c441e2b2#n289 Changes to underlying filesystems --------------------------------- @@ -44,6 +48,23 @@ while the overlay is mounted is not supported: .. _the kernel overlayfs documentation: https://www.kernel.org/doc/html/latest/filesystems/overlayfs.html#changes-to-underlying-filesystems +Unprivileged operation using user namespaces +-------------------------------------------- + +Since Linux 5.11, overlayfs can be mounted in unprivileged user namespaces. +This means that it is possible to temporarily place an overlay in a local +context. For example, ``unshare -Umc --keep-caps sh -c 'tmpoverlay . && exec +setpriv --inh-caps=-all $SHELL'`` has a similar effect to ``tmpoverlay .``, but +does not require privileges. In exchange, it only takes effect within the newly +started shell, similar to environment variables. + +Note that tmpfs overlay doesn't work properly with unmapped UIDs. In other +words, after running tmpoverlay, only files owned by the current user can be +modified; modifying other files will have unpredictable results. + +This issue can be mitigated starting with Linux 5.12 using idmap, but this is +not integrated in tmpoverlay due to a lack of standard utilities. + Pseudo-filesystems ------------------ |