RWTAB(5) Configuration for read-only root file systems RWTAB(5)NAMErwtab - Configuration for read-only root file systems
SYNOPSIS
/etc/rwtab, /etc/rwtab.d
DESCRIPTION
The file /etc/rwtab and additional files in /etc/rwtab.d specify loca‐
tions on a read-only root file system which are made writable by bind
mounting a writable file system at that location. These files are pro‐
cessed at boot time after the local file systems have been mounted.
The following kernel command line options determine how rwtab process‐
ing is done during boot:
readonlyroot Mount the root file system read-only. Process rwtab and
all files in /etc/rwtab.d as described below.
scratch=device Mount device, and remove all files on this file system.
If this option is not specified, a tmpfs file system is
used instead.
state=device Mount device. Alternatively, if a directory is speci‐
fied instead of a device, assume that the directory is
the mount point of a local "auto" mount defined in
/etc/fstab (which is already mounted when this option is
processed).
If this file system contains the files etc/rwtab or
etc/rwtab.d, bind mount these files over /etc/rwtab and
/etc/rwtab.d, respectively, before rwtab processing.
Each line in rwtab files consists of a keyword followed by a pathname.
Empty lines and lines starting with a hash character (#) are ignored.
The following keywords are recognized:
empty Create a new directory pathname and all its parents on
the scratch file system, and bind mount it to pathname.
The pathname must be a directory. If pathname does not
exist on the read-only root file system, do nothing.
dirs Like empty, but copy all directories in the original
pathname to the writable scratch directory before bind
mounting the scratch directory over pathname. Copying
is recursive. The pathname must be a directory.
files Like empty, but copy all files and directories in the
original pathname to the writable scratch directory
before bind mounting the scratch directory over path‐
name. Copying is recursive. The pathname can be a file
or directory.
state If pathname exists on the read-only root file system as
well as on the state file system (see the "state=device"
kernel command line parameter above), bind mount path‐
name on the state mount to pathname on the read-only
root file system.
When INIT_STATE_AUTOMATICALLY is set to "yes" in the
sysconfig file (which is the default), files or direc‐
tories which do not yet exist on the state file system
will be initialized by copying the files on the read-
only root file system to the state file system first.
The state and scratch file systems are mounted as defined in the sycon‐
fig file, and remain mounted at the specified locations (by default
/var/lib/readonlyroot/state and /var/lib/readonlyroot/scratch, respec‐
tively).
WARNING
When a file system is specified as a scratch area with the
"scratch=device" kernel command line parameter, all files on that file
system will be removed at boot time.
BUGS
The way how mount(1) locks /etc/mtab for modification and updates it is
incompatible with a read-only /etc directory. There are two possible
workarounds: (1) convert /etc/mtab into a symlink to /proc/self/mounts
on the read-only root file system, or (2) add the entire /etc directory
to /etc/rwtab. If neither is done, booting will fail.
SEE ALSO
/etc/sysconfig/readonlyroot
COPYRIGHT
2010 SuSE Linux Products GmbH, Nuernberg, Germany.
AUTHOR
Andreas Gruenbacher <agruen@suse.de>
4.2 Berkeley Distribution December 18th, 2010 RWTAB(5)
