fsck, ufs_fsck - Check and repair UFS file systems
/usr/sbin/fsck [fs_options] [filesystem...]
The following options are interpreted by fsck:
Uses the specified block number as the super block for the file system.
Block 32 is usually an alternate super block.
-B Converts UFS Version 4 back to UFS Version 3. When you use the -B
option on a UFS Version 4 file system, it will be marked as a Version 3
file system if there are no files or directories with more than 32767
hardlinks or 32765 subdirectories.
-c If the file system is in the old (static table) format, this option
converts it to the new (dynamic table) format. If the file system is in
the new format, this option converts it to the old format, provided
that the old format can support the file system configuration. In
interactive mode, fsck lists the direction of the conversion and asks
if the conversion should be done. If you answer "no," no further opera-
tions are done on the file system. If the -p option is specified, the
direction of the conversion is listed and the conversion is performed
without user interaction if possible. The -p option should be used if
all the file systems are being converted simultaneously. The format of
a file system can be determined from the first line of output from the
-f Forces fsck to check the root file system, even when the file system is
mounted as writable. Use this option with caution, because running fsck
on a mounted root file system can cause its files to become out of syn-
chronization with running system data. If the problem occurs, the fsck
program displays a message recommending you reboot the system.
Limits the number of parallel checks to the number specified. By
default, the limit is the number of disks running one process per disk.
If a smaller limit is given, the disks are checked using a round
robin-type schedule, one file system at a time.
Uses the mode specified in octal as the permission bits to use when
creating the lost+found directory rather than the default 777. In par-
ticular, systems that do not want to have lost files accessible by all
users on the system should use a more restrictive set of permissions,
such as 700.
-n Answers "no" to all the prompts except for the "CONTINUE?" prompt. The
option does not write to the lost+found file in the file system. If
you do not have write permission on the file system, fsck defaults to
the behavior of the -n option.
-o Causes fsck to unconditionally check the file system even if the file
system's clean byte is set. That is, a file system is checked even if
it has been unmounted cleanly.
-p Noninteractively corrects the following file system inconsistencies:
unreferenced inodes, link counts in inodes that are too large, missing
blocks in the free map, blocks in the free map that are also in files,
and wrong counts in the super-block.
-v Causes more extensive messages to be displayed during the file system
checks (verbose mode).
-y Answers "yes" to all the prompts. This option should be used with cau-
tion because the integrity of the file system data can be corrupted by
answering "yes" to all the prompts.
The fsck command is a front-end program for the ufs_fsck program, which
checks and repairs UFS file systems. Do not use this command for AdvFS file
systems: instead, see advfs(4).
The fsck program has more consistency checks than its check, dcheck,
fcheck, and icheck predecessors combined.
You must be root to use this command.
If you do not specify a file system in the command line, the fsck command
checks the file systems in the /etc/fstab file.
With one exception, the fsck command cannot be used on an active file sys-
tem. The command checks to determine whether the partition to be checked,
or an overlapping partition, is in use. The exceptional case occurs when
you run the command on an active root file system and specify the -f
option. Use this option with caution, because it can cause the data on the
running system (the in-memory data) to become unsynchronized from the file
system data (the on-disk data).
The fsck program interactively repairs inconsistent file system conditions.
If the file system is found to be consistent, the number of files, blocks
used, and free blocks are reported. If the file system is inconsistent,
you are prompted before each correction is attempted. For each corrected
inconsistency, one or more lines are displayed, identifying the file system
on which the correction takes place and the type of correction. After suc-
cessfully correcting a file system, the fsck program displays the number of
files on that file system, the number of used and free blocks, and the per-
centage of fragmentation.
The default behavior of the fsck program is to interactively check the fol-
lowing UFS file system inconsistencies:
Blocks claimed by more than one inode or the free map
Blocks claimed by an inode outside the range of the file system
Incorrect link counts
Size checks: directory size not of proper format; partially truncated file
Bad inode format
Blocks not accounted for anywhere
Directory checks: file pointing to unallocated inode; inode number out of range; . (dot) or .. (dot dot) not the first two entries of a directory or having the wrong inode number
Super Block checks: more blocks for inodes than there are in the file system
Bad free block map format
Total free block and/or free inode count incorrect
If you use the -p option, the fsck program noninteractively attempts to
correct specific file system inconsistencies. The corrections are made
only if they can be done safely. The fsck program can noninteractively
correct the following file system inconsistencies:
Link counts in inodes that are too large
Missing blocks in the free map
Blocks in the free map that are also in files
Wrong counts in the super-block.
If fsck encounters any other inconsistencies, it exits with an abnormal
return status and a subsequent reboot will fail.
The system makes sure that only a restricted class of innocuous incon-
sistencies can occur unless hardware or software failures intervene.
Note that some of the corrective actions can result in a loss of data. The
amount and severity of data lost can be determined from the diagnostic out-
At system boot, fsck -p runs automatically and reads the /etc/fstab file to
determine which file systems to check. Only partitions that are mounted rw
or ro and have a non-zero pass (1 or more) number are checked. File sys-
tems that have a pass number 1 (usually only the root file system) are
checked one at a time. When pass 1 completes, the remaining pass numbers
are processed with one parallel fsck process running per disk drive in the
The per disk drive logic is based on the /dev/disk/dsk0a syntax where dif-
ferent partition letters are treated as being on the same disk drive. Par-
titions layered on top of an LSM device may not follow this naming conven-
tion. Where LSM is used, you can use unique pass numbers in the /etc/fstab
file to sequence the fsck checks.
If a QUIT signal is sent, fsck finishes the file system checks and then
exits with an abnormal return status that causes the automatic reboot to
fail. This is useful if you want to finish the file system checks during an
automatic reboot but do not want the machine to come up multiuser after the
If the fsck default program fails (terminates with a non-zero value), fsck
terminates with the exit value. This ensures that the auto-reboot depen-
dencies, such as those commonly used in the run command script, continue to
If orphaned files or directories (allocated but unreferenced) are found,
you are asked if you want to reconnect the files and directories that are
not empty by putting them in the lost+found directory. The program indi-
cates whether the file or directory is empty or not empty. The fsck pro-
gram reconnects directories that are not empty and assigns the inode number
for the name. If the lost+found directory does not exist, it is created,
and if it has insufficient space, the size is increased. Empty files and
directories are removed unless you specify the -n option.
The following message indicates that the system is avoiding a potential
panic by skipping the file system check:
/dev/disk/dsk2g: skipping filesystem already mounted (read-write) on '/usr'
The following message indicates that the file system is mounted:
/dev/disk/dsk2g on /usr: Device busy
The following message indicates that the partition you are checking is
ERROR: /dev/rdisk/dsk3a or an overlapping partition is open
fsck cannot be run on an active filesystem
The following is an example of an /etc/fstab file that is used in the exam-
ples in this section:
/dev/disk/dsk2a / ufs rw 1 1
/dev/disk/dsk0g /usr ufs rw 1 2
/dev/disk/dsk2b swap1 ufs sw 0 2
/dev/disk/dsk0b /public ufs sw 0 2
/dev/disk/dsk2g /var ufs rw 1 2
/dev/disk/dsk3c /usr/users ufs rw 1 2
The following command checks all the file systems in the /etc/fstab file
but makes no corrections:
# fsck -n
The following example checks a file system found in the /etc/fstab file and
checks a file system that is not found in the /etc/fstab file:
# fsck /dev/rdisk/dsk3c /dev/rdisk/dsk1a
The following command noninteractively checks the file systems in the
# fsck -p
Specifies the command path.
Specifies the command path.
Contains the default list of file systems to check.