fsdb Command
Purpose
Debugs file systems.
Syntax
fsdb FileSystem [ - ]
Description
The fsdb command enables you to examine, alter, and debug a file system, specified by the FileSystem parameter. The command provides access to file system objects,
such as blocks, i-nodes, or directories. You can use the fsdb command to examine and patch damaged file systems. Key components of a file system can be referenced
symbolically. This feature simplifies the procedures for correcting control-block entries and for descending the file system tree.
To examine a file system, specify it by a block device name, a raw device name, or a mounted file system name. In the last case, the fsdb command determines the
associated file system name by reading the /etc/filesystems file. Mounted file systems cannot be modified.
The fsdb command has a different interface for a JFS file system and a JFS2 file system. The following explains how to use fsdb with a JFS file system. See JFS2
Subcommands for information about JFS2 subcommands.
If the file system specified is a JFS2 snapshot, the fsdb command enables examination and modification of the snapshot superblock, snapshot map, block map xtree
copy, and segment headers. See JFS2 Snapshot Subcommands for information about JFS2 snapshot subcommands.
The subcommands for the fsbd command allow you to access, view, or change the information in a file system. Any number you enter in the subcommand is considered
decimal by default, unless you prefix it with either 0 to indicate an octal number or 0x to indicate a hexadecimal number. All addresses are printed in hexadecimal.
Because the fsdb command reads and writes one block at a time, it works with raw as well as with block I/O.
Flag
Item
Description
-
Disables the error checking routines used to verify i-nodes and block addresses. The O subcommand switches these routines on and off. When these routines are
running, the fsdb command reads critical file system data from the superblock. The obtained information allows the fsdb command to access the various file
system objects successfully and to perform various error checks.
Subcommands
The fsdb subcommands are requests to locate and display or modify information in the file system. The main categories of subcommands are:
Item
Description
Category
Function
Location
Access the information in the file system.
Display
View the information in the file system.
Modification
Change the information in the file system.
In addition, there are a few miscellaneous subcommands.
Location Subcommands
There are two types of location subcommands:
Number[ I | M | i | b ]
OR
dDirectorySlot
The first type consists of a number, optionally followed by an address specification. The address specification defines how the preceding number is to be
interpreted. There are four address specifications corresponding to four different interpretations of the Number variable:
Item
Description
I
I-node map block number
M
Disk map block number
i
I-node number
b
Fragment number
Depending on the address specification (or absence of it), this type of location subcommand accesses information as follows:
Item
Description
Number
Accesses data at the absolute byte offset specified by the Number variable.
MapBlockNumberI
Accesses the i-node map block indicated by the MapBlockNumber variable.
MapBlockNumberM
Accesses the disk map block indicated by the MapBlockNumber variable.
InodeNumberi
Accesses the i-node indicated by the InodeNumber variable.
FragmentNumberb
Accesses the file system block indicated by the FragmentNumber variable. A fragment number consists of a block address and an encoded length. A complete
fragment address is 32 bits in length. The low-order 28 bits are the beginning fragment address. The fragment length is encoded in the remaining 4 bits; it is
encoded as the number of fragments less than a full block. For example, on a file system consisting of 1024-byte fragments, the address 0x2000010f references a
block that begins at 1KB block number 0x10f and is 2KB in length. In contrast, on a file system of 512-byte fragments, the address 0x2000010f references a block
that begins at 512-byte block 0x10f and is 3072 (512 * 6) bytes in length.
The second type of location subcommand is used to access directory entries. The subcommand consists of the character d followed by a directory-slot number.
Directory-slot numbers start at 0 for each block of the associated i-node.
This type of location subcommand accesses information as follows:
Item
Description
dDirectorySlot
Accesses the directory entry indexed by the DirectorySlot variable for the current i-node. Only allocated directory entries can be manipulated using this
location subcommand.
Display Subcommands
To view information relative to the address specification, use a display subcommand comprised of one of the display facilities in conjunction with one of the display
formats, as follows:
p[Number]{ i | d | o | e | c | b | y | M | I | x | s | D }
OR
f[Number]{ i | d | o | e | c | b | y | M | I | x | s | D }
The display facilities are:
Item
Description
p
Indicates a general facility. Use the general display subcommand to display data relative to the current address. If you enter a number after the p symbol, the
fsdb command displays that number of entries. A check is made to detect block boundary overflows. If you enter 0 or * (asterisk), the fsdb command displays all
entries to the end of the current fragment.
f
Indicates a file facility. Use the file display subcommand to display data blocks associated with the current i-node. If you enter a number after the f symbol,
the fsdb command displays that block of the file. Block numbering begins at 0. The display format follows the block number. If you enter f without a block
number, the fsdb command defaults to displaying block 0 of the current i-node.
The display formats for either facility are:
Item
Description
i
Displays as i-nodes.
d
Displays as directories.
o
Displays as octal words.
e
Displays as decimal words.
c
Displays as characters.
b
Displays as octal bytes.
y
Displays as hexadecimal bytes.
M
Displays as disk map entries.
I
Displays as i-node map entries.
x
Displays as hexadecimal words.
S
Displays as single indirect blocks.
D
Displays as double indirect blocks.
The chosen display facility and display format remain in effect during the processing of the fsdb command until explicitly changed. You may receive an error message
indicating improper alignment if the address you specify does not fall on an appropriate boundary.
If you use the Number, MapBlockNumberI, or FragmentNumberb location subcommands to access i-node information, you can step through the data, examining each byte,
word, or double word. Select the desired display mode by entering one of the following subcommands:
Item
Description
B
Begins displaying in byte mode.
D
Begins displaying in double-word mode.
W
Begins displaying in word mode.
You can move forward or backward through the information. The boundary advances with the display screen and is left at the address of the last item displayed. The
output can be ended at any time by pressing the INTERRUPT key. The following symbols allow movement through the information:
Item
Description
+ Number
Moves forward the specified number of units currently in effect.
-Number
Moves backward the specified number of units currently in effect.
The following symbols allow you to store the current address and return to it conveniently:
Item
Description
>
Stores the current address.
<
Returns to the previously stored address.
You can use dots, tabs, and spaces as subcommand delimiters, but they are only necessary to delimit a hexadecimal number from a subcommand that could be interpreted
as a hexadecimal digit. Pressing the Enter key (entering a blank line) increments the current address by the size of the data type last displayed. That is, the
address is set to the next byte, word, double word, directory entry, or i-node, allowing you to step through a region of a file system.
The fsdb command displays information in a format appropriate to the data type. Bytes, words, and double words are displayed as a hexadecimal address followed by the
hexadecimal representation of the data at that address and the decimal equivalent enclosed in parentheses. The fsdb command adds a .B or .D suffix to the end of the
address to indicate a display of byte or double word values. It displays directories as a directory slot offset followed by the decimal i-node number and the
character representation of the entry name. It displays i-nodes with labeled fields describing each element. The environment variables control the formats of the
date and time fields.
Modification Subcommands
You can modify information relative to the address specification by using a field specification (for fields in the i-node and fields in the directory). The general
form for assigning new values is: mnemonic operator new-value, where the mnemonic parameter represents one of the fields described in the following list:
The following mnemonics are used for the names of the fields of an i-node and refer to the current working i-node:
Item
Description
md
Permission mode
ln
Link count
uid
User number
gid
Group number
sz
File size
aNumber
Data block numbers (0 to 8) where the Number parameter can be a location subcommand
at
Access time
mt
Modification time
maj
Major device number
min
Minor device number
The following mnemonics refer to the i-node and disk maps:
Item
Description
mf
Map free count
ms
Map size
mp
Permanent allocation bit map
mw
Working allocation bit map
The following mnemonics are used for the names of the fields in directories:
Item
Description
rl
Length of directory entry record
nl
Length of directory name
nm
Directory name
Valid values of the Operator parameter include:
Note: A file system must be unmounted before attempting to modify it.
Item
Description
=
Assigns the New-Value parameter to the specified Mnemonic parameter.
=+
Increment the Mnemonic parameter by the specified New-Value parameter. The default New-Value parameter is a value of one.
=-
Decrease the Mnemonic by the specified New-Value. The default New-Value is a value of one.
="
Assigns the character string specified by the New-Value parameter to the specified Mnemonic parameter. If the current display format is the d address
specification for directory and a mnemonic is not specified, the directory name is changed. The new directory name cannot be longer than the previous directory
name.
Miscellaneous Subcommands
Miscellaneous subcommands are:
Item
Description
q
Quits.
Item
Description
xn
Expands a directory by n bytes where n plus the current size of the directory is not greater than the current directory's fragment in bytes.
!
Escapes to the shell.
O
Toggles error checking.
JFS2 Subcommands
These subcommands can be entered by their entire name or by using a subset of the name. At least the bold letters must be entered.
Item
Description
a[lter] <block> <offset> <hex string>
Alters disk data.
b[map] [<block number>]
Displays block allocation map.
dir[ectory] <inode number> [<fileset>] [R]
Displays directory entries.
d[isplay] [<block> [<offset> [<format> [<count>]]]]
Displays data.
dt[ree] {<block number> |<inode number>{a | f } }
Displays dtree nodes.
h[elp] [<command>]
Provides help on subcommands.
ia[g] [<IAG number>] [a | <fileset>]
Displays IAG pages.
im[ap] [a | <fileset>]
Displays inode allocation map.
i[node] [<inode number>] [a | <fileset>]
Displays inodes.
q[uit]
Exits fsdb.
su[perblock] [p | s]
Displays superblock.
x[tree] {<block number> | <inode number>{a | f}}
Displays xtree nodes.
a[lter] <block> <offset> <hex string>
where:
Item
Description
<block>
block number (decimal)
<offset>
offset within block (hex)
<hex string>
string of hex digits
Alters disk data. <hex string> should contain an even number of digits.
b[map] [<block numbers>]
Display Block Allocation Map.
<block number> Display the dmap page which describes this block number
Subcommands:
Item
Description
m
modify current node
u
visit upper level bmap page
l
visit left sibling
r
visit right sibling
w
display wmap
p
display pmap
s
display stree
x
exit subcommand mode
dir[ectory] <inode number> [<fileset>][R]
Item
Description
<inode number>
inode number of directory (decimal)
<fileset>
number, currently must be zero
R
recursively lists all subdirectories
Displays directory entries.
d[isplay] [<block> [<offset> [<format>[<count>]]]]
Item
Description
<block>
block number (decimal)
<offset>
offset within block (hex)
<format>
format in which to display data (see below)
<count>
number of objects to display (decimal)
Displays data in a variety of formats.
Format may be one of the following:
Item
Description
a
ascii
i
inode struct dinode
I
inode allocation map iag_t
s
superblock struct superblock
x
hexadecimal
dt[ree] {<block number> | <inode number>{a | f}}
Item
Description
<block number>
block number containing a dtree page
<inode number>
inode number of directory (decimal)
{a | f}
'a' indicates inode number is an aggregate inode. 'f' indicates inode number is a fileset inode.
Displays root of the directory btree and enters a subcommand mode in which to navigate the btree.
Subcommands:
Item
Description
m
Modifies current node
f
Walks freelist entries
s
Displays specified slot entry
[0-9]+
Displays specified stbl entry
t
Displays formatted stbl
u
Visits parent node (not parent directory)
d
Visits child node
x
Exits subcommand mode
h[elp] [<command>]
Item
Description
<command>
command name
Prints help text. Lists all commands if no parameter.
ia[g] [<IAG number>] [a | <fileset>]
Item
Description
<IAG number>
IAG number (decimal)
a
use aggregate inode table
<fileset>
fileset number (currently must be zero)
Displays iag information and enters subcommand mode.
Subcommands:
Item
Description
e
Displays/modifies inode extents map
m
Modifies iag
p
Displays/modifies persistent map
w
Displays/modifies working map
im[ap] [a | <fileset>]
Item
Description
a
use aggregate inode table
<fileset>
fileset number (currently must be zero)
Display specified inode map and enters subcommand mode.
Subcommands:
Item
Description
e
Displays/modifies inode extents map
m
Modifies iag
p
Displays/modifies persistent map
i[node] [<inode number>] [a | <fileset>]
Item
Description
<inode number>
Inode number (decimal)
a
Use aggregate inode table
fileset
Fileset number (currently must be zero)
Displays inode information and enters subcommand mode.
Subcommands:
Item
Description
m
Modifies inode
t
Displays/modifies inode's b-tree
e
display/modify inode's EAs
Note: The fsdb command understands both the v1 and the v2 extended attribute formats. The behavior when viewing EAs is dependent on the format for the inode
being viewed.
For v1, after displaying the inode's EAs you can modify its pxdTable or eaDirectory entries. Specify modify option and then the pxdTable or eaDirectory
indicator and the offset into the table.
For v2 the EAs are displayed using the dtree subcommand format. All of the dtree subcommands are then available for further action on the EAs.
q[uit]
Exits fsdb.
su[perblock] [p | s]
Item
Description
p
Displays primary superblock
s
Displays secondary superblock
Displays superblock data.
x[tree] {<block number> | <inode number>{a | f} }
Item
Description
<block number>
block number (decimal)
<inode number>
inode number
{a | f}
'a' indicates inode number is an aggregate inode. 'f' indicates inode number is a fileset inode.
Displays one node of a xtree and enters a subcommand mode in which to navigate the xtree.
Subcommands:
Item
Description
m
Modifies current node
u
Visits parent node
d
Visits child node
n
Visits right sibling
p
Visits left sibling
s
Selects xad entry to view
x
Exits subcommand mode
JFS2 Snapshot Subcommands
These subcommands can be entered by their entire name or by using a subset of the name. At least the bold letters must be entered.
Item
Description
a[lter] <block> <offset> <hex string>
Alters disk data.
b[map]
Displays block map xtree copy.
d[isplay] [<block> [<offset> [<format> [<count>]]]]
Displays data.
h[elp] [<command>]
Provides help on subcommands.
q[uit]
Exits fsdb.
st[able] [<block number>]
Displays summary snapshot table.
s[map] <block number>
Displays snapshot bit map.
su[perblock]
Displays superblock.
a[lter] <block> <offset> <hex string>
where:
Item
Description
<block>
block number (decimal)
<offset>
offset within block (hex)
<hex string>
string of hex digits
Alters disk data. <hex string> should contain an even number of digits.
b[map]
Displays block map xtree copy.
d[isplay] [<block> [<offset> [<format>[<count>]]]]
Item
Description
<block>
block number (decimal)
<offset>
offset within block (hex)
<format>
format in which to display data (see below)
<count>
number of objects to display (decimal)
Displays data in a variety of formats.
Format may be one of the following:
Item
Description
a
ascii
s
snapshot segment header
t
snapshot table page
x
xtree page
h[elp] [<command>]
Item
Description
<command>
command name
Provides help on subcommands.
q[uit]
Exits fsdb.
st[able] [<block number>]
where:
Item
Description
<block number>
block number (decimal)
Displays summary snapshot table.
s[map] [<block number>]
where:
Item
Description
<block number>
block number (decimal)
Displays snapshot bit map.
su[perblock]
Displays superblock.
Security
Attention RBAC users and Trusted AIX users: This command can perform privileged operations. Only privileged users can run privileged operations. For more information
about authorizations and privileges, see Privileged Command Database in Security. For a list of privileges and the authorizations associated with this command, see
the lssecattr command or the getcmdattr subcommand.
Examples
The following examples show subcommands you can use after starting the fsdb command on a JFS file system.
1 To display an i-node, enter:
386i
This command displays i-node 386 in i-node format. It now becomes the current i-node.
2 To change the link count for the current i-node to a value of 4, enter:
ln=4
3 To increase the link count of the current i-node by a value of 1, enter:
ln=+1
4 To display part of the file associated with the current i-node, enter:
fc
This command displays block 0 of the file associated with the current i-node in ASCII bytes.
5 To display entries of a directory, enter:
2i.fd
This changes the current i-node to the root i-node (i-node 2) and then displays the directory entries in the first block associated with that i-node. One or
more of the last entries displayed may have an i-node number of 0 (zero). These are unused directory blocks; such entries cannot be manipulated as in the next
example.
6 To go down a level of the directory tree, enter:
d5i.fc
This command changes the current i-node to the one associated with directory entry 5. Then it displays the first block of the file as ASCII text (fc). Directory
entries are numbered starting from 0.
7 To display a block when you know its block number, enter:
1b.p0o
This command displays the superblock (block 1) of file system in octal.
8 To change the i-node of a directory entry, enter:
2i.a0b.d7=3
This command changes the i-node of directory entry 7 in the root directory (2i) to 3. This example also shows how several operations can be combined on one
line.
9 To change the file name of a directory entry, enter:
d7.nm="chap1.rec"
This command changes the name field of directory entry 7 to chap1.rec.
10 To display a given block of the file associated with the current i-node, enter:
a2b.p0d
This command displays block 2 of the current i-node as directory entries.
11 To display the content of a single indirect block at block 7, enter:
7b. p0S
This command displays the block numbers allocated to the i-node that has a single indirect block at block 7.
12 To display the first page of the disk map, enter:
OM
13 To display the first 10 words of permanent block allocation map in hexadecimal, enter:
mp1.p10x
This command shows the allocation bit map at the current address; for example, at 0M.
The following examples show some subcommands you can use on a JFS2 file system. Attention: Do not use JFS2 subcommands to modify a file system.
1 To display an i-node, enter:
inode 2
This command displays i-node 2 in i-node format.
2 To display entries of a directory, enter:
dir 2
This command displays the directory entries associated with i-node 2.
3 To display a block whose block number is 0x1000, enter:
display 0x1000
This command displays the block at file system in hexadecimal format.
Files
Item
Description
/usr/sbin
Contains the fsdb command.
/etc/filesystems
Contains information on the file systems.
