nilfs

NILFS(8) System Manager's Manual NILFS(8)

NAME

   NILFS - the new implementation of a log-structured file system

SYNOPSIS

   Overview of the NILFS file system and the related tools.

DESCRIPTION

   NILFS  is  a  log-structured  file  system developed for Linux.  NILFS provides versioning capability of an entire file system and continuous snapshotting that allows users to restore
   files mistakenly overwritten or destroyed a while ago.

   The current major version of NILFS is version 2, which is referred to as NILFS2.  NILFS2 is equipped with an online garbage collector (also called cleaner) that reclaims disk space in
   the background with keeping multiple snapshots.

   When data is written or any change is made to a NILFS2 file system, it automatically creates a checkpoint.  A checkpoint represents a consistent state of the NILFS2 file system  of  a
   certain  instant.   It becomes mountable after being changed into a snapshot.  A snapshot is the checkpoint marked not to be deleted by the cleaner.  NILFS2 creates a number of check‐
   points at regular intervals (unless there is no change) or with synchronous writings.  There is no practical limit on the number of checkpoints and snapshots.

   The following tools are available to manage the checkpoint and the snapshot:

   lscp        lists checkpoints or snapshots

   mkcp        makes a checkpoint or a snapshot

   chcp        changes an existing checkpoint to a snapshot or vice versa

   rmcp        invalidates specified checkpoint(s)

   These tools give the versioning capability to NILFS2; a user can select significant versions among continuously created checkpoints and can change them to snapshots  to  be  preserved
   for long periods.

   Every  checkpoint  except for the snapshot will become unprotected from the cleaner after a given period of time.  This period is controlled by the protection_period parameter defined
   in the /etc/nilfs_cleanerd.conf(5) file.

MOUNT OPTIONS

   Refer to the mount.nilfs2(8).

EXAMPLES

   mkfs -t nilfs2 /dev/sdb1
          creates a NILFS2 file system on a block device `/dev/sdb1'.

   mount -t nilfs2 /dev/sdb1 /nilfs
          mounts the NILFS2 file system on a mount point `/nilfs' like an ordinary POSIX file system.  This will invoke a cleaner process nilfs_cleanerd(8) through an external mount pro‐
          gram (i.e. mount.nilfs2(8)).

   lscp   lists checkpoints created in the file system as follows:

           CNO        DATE     TIME  MODE  FLG      BLKCNT       ICNT
             1  2014-01-18 20:49:54   cp    -            4          2
             2  2014-01-18 20:51:45   cp    -         3990         11
             3  2014-01-18 20:51:45   cp    -         6058          3
             4  2014-01-18 20:51:49   cp    -         4807          6
             5  2014-01-18 20:51:49   cp    -          262          3
           ...

   chcp ss 2
          changes the checkpoint whose checkpoint-number is two to a snapshot.  Then the checkpoint list will become as follows:

           CNO        DATE     TIME  MODE  FLG      BLKCNT       ICNT
             1  2014-01-18 20:49:54   cp    -            4          2
             2  2014-01-18 20:51:45   ss    -         3990         11
             3  2014-01-18 20:51:45   cp    -         6058          3
             4  2014-01-18 20:51:49   cp    -         4807          6
             5  2014-01-18 20:51:49   cp    -          262          3
           ...

   mount -t nilfs2 -r -o cp=2 /dev/sdb1 /snapshot
          mounts the snapshot on another directory `/snapshot' as a read-only file system.  Here the snapshot mount requires at least two options, a read-only option (-r or  -o  ro)  and
          the cp option (-o cp=checkpoint-number).  Note that a read/write mount and one or more snapshots are mountable independently, so the online backup is possible through the snap‐
          shot mounts.

           # mount -t nilfs2
           /dev/sdb1 on /nilfs type nilfs2 (rw,gcpid=13296)
           /dev/sdb1 on /snapshot type nilfs2 (ro,cp=2)

   umount /nilfs
          unmounts the NILFS2 file system mounted on `/nilfs' and will shutdown the nilfs_cleanerd(8) through an external umount program (umount.nilfs2(8)) for the read/write mount.

AUTHORS

   NILFS2 was developed by NILFS development team.