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Topic review - How to read UFS filesystem super block information in FreeBSD
Author Message
Post subject: How to read UFS filesystem super block information in FreeBSD  |  Post Posted: Mon Jul 22, 2013 9:52 am
How to read UFS filesystem super block information in FreeBSD

Use the dumpfs utility (by default in FreeBSD). Quote from man:
Quote:
# man dumpfs
DUMPFS(8) FreeBSD System Manager's Manual DUMPFS(8)

NAME
dumpfs -- dump UFS file system information

SYNOPSIS
dumpfs [-f] [-l] [-m] filesys | device

DESCRIPTION
The dumpfs utility prints out the UFS super block and cylinder group
information for the file system or special device specified, unless the
-f, -l or -m flag is specified. The listing is very long and detailed.
This command is useful mostly for finding out certain file system infor-
mation such as the file system block size and minimum free space percent-
age.

If -f is specified, a sorted list of all free fragments and free fragment
ranges, as represented in cylinder group block free lists, is printed.
If the flag is specified twice, contiguous free fragments are not col-
lapsed into ranges and instead printed in a simple list. Fragment num-
bers may be converted to raw byte offsets by multiplying by the fragment
size, which may be useful when recovering deleted data.

If -l is specified, the pathname to the file system's container derived
from its unique identifier is printed.

If -m is specified, a newfs(8) command is printed that can be used to
generate a new file system with equivalent settings.

SEE ALSO
disktab(5), fs(5), disklabel(8), fsck(8), newfs(8), tunefs(8)

HISTORY
The dumpfs utility appeared in 4.2BSD.

FreeBSD 9.1 Jul 14, 2011 FreeBSD 9.1



Reading /var filesystem superblock information with dumpfs:
Code:
# dumpfs /var | less
magic   19540119 (UFS2) time    Mon Jul 22 13:50:48 2013
superblock location     65536   id      [ 4fa661e4 f7c0aa2c ]
ncg     20      size    3670016 blocks  3610471
bsize   32768   shift   15      mask    0xffff8000
fsize   4096    shift   12      mask    0xfffff000
frag    8       shift   3       fsbtodb 3
minfree 8%      optim   time    symlinklen 120
maxbsize 32768  maxbpg  4096    maxcontig 4     contigsumsize 4
nbfree  205903  ndir    44112   nifree  643408  nffree  55447
bpg     23680   fpg     189440  ipg     47360   unrefs  0
nindir  4096    inopb   128     maxfilesize     2252349704110079
sbsize  4096    cgsize  32768   csaddr  3000    cssize  4096
sblkno  24      cblkno  32      iblkno  40      dblkno  3000
cgrotor 13      fmod    0       ronly   0       clean   0
avgfpdir 64     avgfilesize 16384
flags   soft-updates+journal
fsmnt   /
volname         swuid   0       providersize    0

cs[].cs_(nbfree,ndir,nifree,nffree):
        (3644,102,44949,1494) (21376,261,44596,3772) (16132,3770,29881,3797) (18437,1371,40690,7041)
        (10937,1835,30612,17343) (12519,985,37439,2427) (19055,25,46948,633) (12,1450,28024,2792)
        (533,3024,30662,2020) (1043,459,32951,2339) (5271,698,16416,568) (4844,4157,24950,73)
        (6822,4462,25282,1688) (17383,329,43333,2771) (19817,1245,36241,1832) (20501,2313,34224,2367)
        (14562,4447,23975,701) (7377,4332,24014,397) (2475,4562,21280,847) (3163,4285,26941,545)
blocks in last group 8832


cg 0:
magic   90255   tell    20000   time    Wed Jul  3 13:34:44 2013
cgx     0       ndblk   189440  niblk   47360   initiblk 47360  unrefs 0
nbfree  3644    ndir    102     nifree  44949   nffree  1494
rotor   26224   irotor  5       frotor  11792
frsum   158     144     62      54      45      48      19
sum of frsum: 1494
clusters 1-3:   37      18      11
....

Rest of the output is ommited to keep the post short.
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