[systemd-devel] early mounts in systemd

[Norbert Lange]

I believe you can have a hard time if you dont do (the last step
atleast) with a var.mount file.
The mount files are special as systemd will pull those up implicitly
if they are needed.

Maybe you could rework your solution, so that one service mounts your
first or second choice in
a separate directory (/run/mymount) then you add a var.mount unit that
depends ("BindsTo") on said service
and bind-mounts /run/mymount to var.
That way you will hook into the existing systemd machinery.

I did something similar with an overlayfs once. Tested to work correctly,
even if you have further mounts like /var/tmp (systemd should
automatically add dependency to var.mount).

Norbert

# file rootfs-bindmount-var.service
[Unit]
Description=Bind-mount variable storage (/var)
Documentation=man:file-hierarchy(7)
ConditionPathIsSymbolicLink=!/var
# ConditionPathIsReadWrite=!/var
DefaultDependencies=no
Conflicts=umount.target
Before=local-fs.target umount.target
After=local-fs-pre.target

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStartPre=-/bin/mkdir /run/varoverlay
ExecStartPre=/bin/mount --make-private -n -t tmpfs tmpfs_root_ovl
/run/varoverlay
ExecStartPre=/bin/mkdir /run/varoverlay/lower /run/varoverlay/upper
/run/varoverlay/work
ExecStart=/bin/mount --make-private -n --bind /var /run/varoverlay/lower
ExecStop=/bin/umount -n /run/varoverlay/lower
ExecStopPost=/bin/umount -n /run/varoverlay
ExecStopPost=/bin/rmdir /run/varoverlay


# file var.mount
[Unit]
Description=variable storage (/var)
Documentation=man:file-hierarchy(7)
ConditionPathIsSymbolicLink=!/var
ConditionPathIsReadWrite=!/var
After=rootfs-bindmount-var.service
BindsTo=rootfs-bindmount-var.service

[Mount]
What=overlay_var
Where=/var
Type=overlay
Options=lowerdir=/run/varoverlay/lower,upperdir=/run/varoverlay/upper,workdir=/run/varoverlay/work,redirect_dir=on,index=on,xino=on