Ubuntu Manpage: NILFS - the new implementation of a log-structured file system

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 checkpoints 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 program (i.e. mount.nilfs2(8)).

       lscp   lists checkpoints created in the file system as follows:

               CNO        DATE     TIME  MODE  FLG   NBLKINC       ICNT
                 1  2008-05-08 14:45:49   cp    -         11          2
                 2  2008-05-08 14:50:22   cp    -     200523         81
                 3  2008-05-08 20:40:34   cp    -        136         61
                 4  2008-05-08 20:41:20   cp    -     187666       1604
                 5  2008-05-08 20:41:42   cp    -         51       1634
               ...

       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   NBLKINC       ICNT
                 1  2008-05-08 14:45:49   cp    -         11          2
                 2  2008-05-08 14:50:22   ss    -     200523         81
                 3  2008-05-08 20:40:34   cp    -        136         61
                 4  2008-05-08 20:41:20   cp    -     187666       1604
                 5  2008-05-08 20:41:42   cp    -         51       1634
               ...

       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 snapshot 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.

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