ReferenceInformation-oriented

Mount options

The cetrafs mount options, the read-only observer mode, the cluster-wide file-lock mode, and remount rules.

mount -t cetrafs [-o OPTIONS] <dev> <mountpoint>

Options

Option	Effect
(default)	Read-write cluster participant. The cross-node exclusive open lock is on: while a node has a file open for writing, any open of that file from another node fails with `ETXTBSY`.
`nofilelock`	Turns the automatic exclusive open lock off, so an image can be open on two nodes during a live-migration handoff. File metadata is then read fresh from the device on every access. The defragmenter is disabled. Per-file locking is still available through `flock(2)`. Applies to the whole cluster; see below.
`ro`	Read-only observer. Registers and heartbeats, so peers don’t reclaim files it is reading, and publishes read presence. Claims no Zone Group, replays no journal, runs no defragmenter or scrubber, and writes nothing else.

noatime is always in force; reads never update access times.

The first node to mount while no other node has the volume mounted (the lead) sets the mode.
Nodes that mount later inherit the mode, whatever options they pass, unless they pass a conflicting one.
A conflicting option (for example nofilelock when the cluster is locked) fails the mount with EINVAL and a log message.
When every node has unmounted, the mode is forgotten.
/proc/fs/cetrafs/<dev>/info shows the mode in effect as file_lock: on|off.

Change	Allowed?
`remount,ro` / `remount,rw`	Refused. Unmount and mount again.
Adding or removing `nofilelock`	Refused. Unmount and mount again.

Error	Cause
`EBUSY`	The device has no atomic CAW and another live node already has it mounted.
`EINVAL`	Format version or incompatible feature not understood; file-lock mode conflicts with the cluster; or the region map failed validation. `dmesg` says which.
Refused, with “CAW discovery failed” in `dmesg`	cetrafs couldn’t determine whether the device supports compare-and-write, so it won’t guess.
Read-only mount when read-write was asked for	An unknown read-only-compatible feature bit is set on the volume.

Call	Result
`flock(fd, LOCK_EX)`	Claims the cross-node exclusive lock. No other node can open the file while it is held.
`flock(fd, LOCK_UN)` or closing all duplicates of the fd	Releases it
`flock(fd, LOCK_SH)`	`EOPNOTSUPP`: only exclusive locks exist
Any `flock` on a default (locked) mount	`EOPNOTSUPP`: the lock is already automatic

Last updated 21 October 2026