LPI Linux Certification in a Nutshell (27 page)

xfs_info

xfs_info
device

XFS is a filesystem type that was originally designed
for use on the IRIX operating system. It has been ported to Linux
and is a popular choice among Linux users for its large filesystem
capacity and robust feature set. The
xfs_info
program will print out information about the XFS partition.

Create an XFS filesystem on
/dev/sdb1
:

#
mkfs.xfs –q /dev/sdb1

Query the filesystem for information:

#
xfs_info /dev/sdb1
meta-data=/dev/sdb1              isize=256    agcount=4, agsize=490108 blks
=                       sectsz=512   attr=2
data     =                       bsize=4096   blocks=1960432, imaxpct=25
=                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0
log      =internal               bsize=4096   blocks=2560, version=2
=                       sectsz=512   sunit=0 blks, lazy-count=0
realtime =none                   extsz=4096   blocks=0, rtextents=0

fsck

fsck [
options
] [-t
type
] [
fs-options
]
filesystems

Check
filesystems
for
errors and optionally correct them. By default,
fsck
assumes the
ext2
filesystem type and runs interactively, pausing to ask for
permission before applying fixes.

Check the
ext3
filesystem on
/dev/sda1
, which is not mounted:

#
fsck /dev/sda1
fsck 1.41.4 (27-Jan-2009)
e2fsck 1.41.4 (27-Jan-2009)
/boot: clean, 48/50200 files, 41926/200780 blocks

The partition was clean, so
fsck
didn’t
really check it.

Force a check:

#
fsck -f /dev/sda1
fsck 1.41.4 (27-Jan-2009)
e2fsck 1.41.4 (27-Jan-2009)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/boot: 48/50200 files (22.9% non-contiguous), 41926/200780 blocks

Force another check, this time with verbose output:

#
fsck -fv /dev/sda1
fsck 1.41.4 (27-Jan-2009)
e2fsck 1.41.4 (27-Jan-2009)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
48 inodes used (0.10%)
11 non-contiguous files (22.9%)
0 non-contiguous directories (0.0%)
# of inodes with ind/dind/tind blocks: 22/12/0
41926 blocks used (20.88%)
0 bad blocks
0 large files
32 regular files
6 directories
0 character device files
0 block device files
0 fifos
0 links
1 symbolic link (1 fast symbolic link)
0 sockets
--------
39 files

Allow
fsck
to automatically perform all
repairs on a damaged filesystem by specifying the
-y
option to run the command
automatically:

#
fsck -y /dev/sda1
fsck 1.41.4 (27-Jan-2009)
e2fsck 1.41.4 (27-Jan-2009)
Couldn't find ext2 superblock, trying backup blocks...
/dev/sda1 was not cleanly unmounted, check forced.
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
Block bitmap differences:  +1 +2 +3 +4
Fix? yes
Inode bitmap differences:  +1 +2 +3 +4 +5 +6
Fix? yes
/dev/sda1: ***** FILE SYSTEM WAS MODIFIED *****
/dev/sda1: 1011/34136 files (0.1% non-contiguous), 4360/136521 blocks

When Linux boots, the kernel performs a check of all
filesystems in
/etc/fstab
using the
-A
option to
fsck
(unless
the
/etc/fstab
entry contains the
noauto
option). Any filesystems that were not
cleanly unmounted are checked. If that check finds any significant
errors, the system drops into single-user mode so you can run
fsck
manually. Unfortunately, unless you have
detailed knowledge of the inner workings of the filesystem, there’s
little you can do other than to have
fsck
perform all of the repairs. As a result, it is common to use the
-y
option and hope for the best.

In some cases, a filesystem may be beyond repair or may even
trigger a bug in
e2fsck
. In these (thankfully
very
rare) situations, there are a few commands
that can help an
ext2
filesystem wizard debug
the problem. These commands are
e2image,
dumpe2fs
, and
debugfs
. For more
information on these tools, read their appropriate manpages.

xfs_metadump

xfs_metadump [
options
]
device

xfs_metadump
is a debugging tool
that copies the metadata from an XFS filesystem to a file. This is
useful as a debugging tool when you suspect filesystem problems, or
as a backup tool. Images created by
xfs_metadump
can be restored to a filesystem
using the command
xfs_mdre
store
.

Since the Linux filesystem hierarchy is spread across
separate partitions and/or multiple drives, it is necessary to
automatically mount those filesystems at boot time. In addition,
removable media and filesystems on remote NFS servers may be used
regularly with recurring mount properties. All of this information is
recorded in the
/etc/fstab
file.
Filesystems defined in this file are checked and mounted when the system
boots. Entries in this file are consulted for default information when
users wish to mount removable media.

The
/etc/fstab
file (see
Example 7-1
) is plain text and
consists of lines with six fields:

/dev/sda1      /                ext2    defaults        1 1
/dev/sda5      /boot            ext2    defaults        1 2
/dev/sda9      /home            ext2    defaults        1 2
/dev/sda6      /root            ext2    defaults        1 2
/dev/sda10     /tmp             ext2    defaults        1 2
/dev/sda8      /usr             ext2    defaults        1 2
/dev/sda7      /var             ext2    defaults        1 2
/dev/sda11     swap             swap    defaults        0 0
/dev/fd0       /mnt/floppy      ext2    noauto,users    0 0
/dev/hdc       /mnt/cdrom       iso9660 noauto,ro,users 0 0
/dev/hdd       /mnt/zip         vfat    noauto,users    0 0
fs1:/share     /fs1             nfs     defaults        0 0

The
fstab
in
Example 7-1
depicts a system with a
single SCSI disk,
/dev/sda
. The first partition,
/dev/sda1
, contains an
ext2
root filesystem. Partition
/dev/sda11
is swap.
Partitions
/dev/sda5
through
/dev/sda10
contain
ext2
filesystems for
/boot
,
/home
,
/root
,
/tmp
,
/usr
, and
/var
, respectively. All of the local
ext2
partitions are to be checked by
fsck
and dumped. Entries for the floppy disk
(
/dev/fd0
), CD-ROM (
/dev/hdc
), and IDE Zip drive
(
/dev/hdd
) hold appropriate mount properties,
making manual mounting of these devices simple. Finally, this example
shows a remote NFS mount of directory
/share
of
system
fs1
. It is mounted locally at
/fs1
.

The
/etc/fstab
file is automatically created
when Linux is installed and is based on the partitioning and mount point
configuration specified. This file can be changed at any time to add
devices and options, tailoring the filesystem to meet your specific
needs.

Filesystems are mounted using the
mount
command. At boot time, those filesystems with
a nonzero pass number in
/etc/fstab
are checked and
automatically mounted. Later, you can run
mount
manually to add other filesystems to the filesystem
hierarchy
.

Filesystems can be unmounted using the
umount
command. When a filesystem is
unmounted, the buffers of the filesystem are synchronized with the
actual contents on disk and the filesystem is made unavailable, freeing
the
mount point. If the filesystem is busy,
umount
yields an error. This will happen, for
example, when the filesystem contains open files or when a process has a
working directory within the filesystem. Other less obvious errors can
occur when removable media are exchanged without being unmounted
first.