From e0a634d520d9cd113d06142ae681f411b609c550 Mon Sep 17 00:00:00 2001 From: Lennart Poettering Date: Thu, 6 Mar 2025 16:06:35 +0100 Subject: [PATCH] docs: mention when /var/ has to be writable In light of https://github.com/systemd/systemd/issues/36635 let's clarify things a bit regarding writability of /var/. --- docs/MOUNT_REQUIREMENTS.md | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/docs/MOUNT_REQUIREMENTS.md b/docs/MOUNT_REQUIREMENTS.md index 9ccbd089bf..7f61b41ff4 100644 --- a/docs/MOUNT_REQUIREMENTS.md +++ b/docs/MOUNT_REQUIREMENTS.md @@ -59,6 +59,14 @@ initrd), and require some late boot service (for example a network manager implementation) to operate this will likely result in cyclic ordering dependencies, and will result in various forms of boot failures. +Also note that the whole of `/var/` (including `/var/tmp/`), and `/tmp/` must +be *writable* at the moment indicated above. It's OK if they are mounted +read-only at an earlier time as long as they are remounted writable by the +indicated point in time. Systems where these three hierarchies remain read-only +during regular operation are not supported by `systemd`. (Note that for +stateless systems it is absolutely OK and supported to mount an empty `tmpfs` +there at boot, `systemd` will know how to populate the tree as necessary.) + If you intend to use network-backed mounts (NFS, SMB, iSCSI, NVME-TCP and similar, including anything you add the `_netdev` pseudo mount option to) for any of the mounts from category 1 or 2, make sure to use a network managing