| 3.t (96707) | 3.t (102231) |
|---|---|
| 1.\" Copyright (c) 1982, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. --- 15 unchanged lines hidden (view full) --- 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" | 1.\" Copyright (c) 1982, 1993 2.\" The Regents of the University of California. All rights reserved. 3.\" 4.\" Redistribution and use in source and binary forms, with or without 5.\" modification, are permitted provided that the following conditions 6.\" are met: 7.\" 1. Redistributions of source code must retain the above copyright 8.\" notice, this list of conditions and the following disclaimer. --- 15 unchanged lines hidden (view full) --- 24.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 25.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 26.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 27.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 28.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 29.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 30.\" SUCH DAMAGE. 31.\" |
| 32.\" $FreeBSD: head/sbin/fsck_ffs/SMM.doc/3.t 96707 2002-05-16 04:10:46Z trhodes $ | 32.\" $FreeBSD: head/sbin/fsck_ffs/SMM.doc/3.t 102231 2002-08-21 18:11:48Z trhodes $ |
| 33.\" @(#)3.t 8.1 (Berkeley) 6/5/93 34.\" | 33.\" @(#)3.t 8.1 (Berkeley) 6/5/93 34.\" |
| 35.ds RH Fixing corrupted filesystems | 35.ds RH Fixing corrupted file systems |
| 36.NH | 36.NH |
| 37Fixing corrupted filesystems | 37Fixing corrupted file systems |
| 38.PP | 38.PP |
| 39A filesystem | 39A file system |
| 40can become corrupted in several ways. 41The most common of these ways are 42improper shutdown procedures 43and hardware failures. 44.PP 45File systems may become corrupted during an 46.I "unclean halt" . 47This happens when proper shutdown 48procedures are not observed, | 40can become corrupted in several ways. 41The most common of these ways are 42improper shutdown procedures 43and hardware failures. 44.PP 45File systems may become corrupted during an 46.I "unclean halt" . 47This happens when proper shutdown 48procedures are not observed, |
| 49physically write-protecting a mounted filesystem, 50or a mounted filesystem is taken off-line. | 49physically write-protecting a mounted file system, 50or a mounted file system is taken off-line. |
| 51The most common operator procedural failure is forgetting to 52.I sync 53the system before halting the CPU. 54.PP 55File systems may become further corrupted if proper startup 56procedures are not observed, e.g., | 51The most common operator procedural failure is forgetting to 52.I sync 53the system before halting the CPU. 54.PP 55File systems may become further corrupted if proper startup 56procedures are not observed, e.g., |
| 57not checking a filesystem for inconsistencies, | 57not checking a file system for inconsistencies, |
| 58and not repairing inconsistencies. | 58and not repairing inconsistencies. |
| 59Allowing a corrupted filesystem to be used (and, thus, to be modified | 59Allowing a corrupted file system to be used (and, thus, to be modified |
| 60further) can be disastrous. 61.PP 62Any piece of hardware can fail at any time. 63Failures 64can be as subtle as a bad block 65on a disk pack, or as blatant as a non-functional disk-controller. 66.NH 2 67Detecting and correcting corruption --- 14 unchanged lines hidden (view full) --- 82.I fsck_ffs 83reports the inconsistency for the operator to 84chose a corrective action. 85.PP 86A quiescent\(dd 87.FS 88\(dd I.e., unmounted and not being written on. 89.FE | 60further) can be disastrous. 61.PP 62Any piece of hardware can fail at any time. 63Failures 64can be as subtle as a bad block 65on a disk pack, or as blatant as a non-functional disk-controller. 66.NH 2 67Detecting and correcting corruption --- 14 unchanged lines hidden (view full) --- 82.I fsck_ffs 83reports the inconsistency for the operator to 84chose a corrective action. 85.PP 86A quiescent\(dd 87.FS 88\(dd I.e., unmounted and not being written on. 89.FE |
| 90filesystem may be checked for structural integrity | 90file system may be checked for structural integrity |
| 91by performing consistency checks on the | 91by performing consistency checks on the |
| 92redundant data intrinsic to a filesystem. | 92redundant data intrinsic to a file system. |
| 93The redundant data is either read from | 93The redundant data is either read from |
| 94the filesystem, | 94the file system, |
| 95or computed from other known values. | 95or computed from other known values. |
| 96The filesystem | 96The file system |
| 97.B must 98be in a quiescent state when 99.I fsck_ffs 100is run, 101since 102.I fsck_ffs 103is a multi-pass program. 104.PP 105In the following sections, 106we discuss methods to discover inconsistencies 107and possible corrective actions 108for the cylinder group blocks, the inodes, the indirect blocks, and 109the data blocks containing directory entries. 110.NH 2 111Super-block checking 112.PP | 97.B must 98be in a quiescent state when 99.I fsck_ffs 100is run, 101since 102.I fsck_ffs 103is a multi-pass program. 104.PP 105In the following sections, 106we discuss methods to discover inconsistencies 107and possible corrective actions 108for the cylinder group blocks, the inodes, the indirect blocks, and 109the data blocks containing directory entries. 110.NH 2 111Super-block checking 112.PP |
| 113The most commonly corrupted item in a filesystem | 113The most commonly corrupted item in a file system |
| 114is the summary information 115associated with the super-block. 116The summary information is prone to corruption 117because it is modified with every change to the file 118system's blocks or inodes, 119and is usually corrupted 120after an unclean halt. 121.PP --- 6 unchanged lines hidden (view full) --- 128The file-system size and layout information 129are the most critical pieces of information for 130.I fsck_ffs . 131While there is no way to actually check these sizes, 132since they are statically determined by 133.I newfs , 134.I fsck_ffs 135can check that these sizes are within reasonable bounds. | 114is the summary information 115associated with the super-block. 116The summary information is prone to corruption 117because it is modified with every change to the file 118system's blocks or inodes, 119and is usually corrupted 120after an unclean halt. 121.PP --- 6 unchanged lines hidden (view full) --- 128The file-system size and layout information 129are the most critical pieces of information for 130.I fsck_ffs . 131While there is no way to actually check these sizes, 132since they are statically determined by 133.I newfs , 134.I fsck_ffs 135can check that these sizes are within reasonable bounds. |
| 136All other filesystem checks require that these sizes be correct. | 136All other file system checks require that these sizes be correct. |
| 137If 138.I fsck_ffs 139detects corruption in the static parameters of the default super-block, 140.I fsck_ffs 141requests the operator to specify the location of an alternate super-block. 142.NH 2 143Free block checking 144.PP 145.I Fsck_ffs 146checks that all the blocks 147marked as free in the cylinder group block maps 148are not claimed by any files. 149When all the blocks have been initially accounted for, 150.I fsck_ffs 151checks that 152the number of free blocks 153plus the number of blocks claimed by the inodes | 137If 138.I fsck_ffs 139detects corruption in the static parameters of the default super-block, 140.I fsck_ffs 141requests the operator to specify the location of an alternate super-block. 142.NH 2 143Free block checking 144.PP 145.I Fsck_ffs 146checks that all the blocks 147marked as free in the cylinder group block maps 148are not claimed by any files. 149When all the blocks have been initially accounted for, 150.I fsck_ffs 151checks that 152the number of free blocks 153plus the number of blocks claimed by the inodes |
| 154equals the total number of blocks in the filesystem. | 154equals the total number of blocks in the file system. |
| 155.PP 156If anything is wrong with the block allocation maps, 157.I fsck_ffs 158will rebuild them, 159based on the list it has computed of allocated blocks. 160.PP 161The summary information associated with the super-block | 155.PP 156If anything is wrong with the block allocation maps, 157.I fsck_ffs 158will rebuild them, 159based on the list it has computed of allocated blocks. 160.PP 161The summary information associated with the super-block |
| 162counts the total number of free blocks within the filesystem. | 162counts the total number of free blocks within the file system. |
| 163.I Fsck_ffs 164compares this count to the | 163.I Fsck_ffs 164compares this count to the |
| 165number of free blocks it found within the filesystem. | 165number of free blocks it found within the file system. |
| 166If the two counts do not agree, then 167.I fsck_ffs 168replaces the incorrect count in the summary information 169by the actual free-block count. 170.PP 171The summary information | 166If the two counts do not agree, then 167.I fsck_ffs 168replaces the incorrect count in the summary information 169by the actual free-block count. 170.PP 171The summary information |
| 172counts the total number of free inodes within the filesystem. | 172counts the total number of free inodes within the file system. |
| 173.I Fsck_ffs 174compares this count to the number | 173.I Fsck_ffs 174compares this count to the number |
| 175of free inodes it found within the filesystem. | 175of free inodes it found within the file system. |
| 176If the two counts do not agree, then 177.I fsck_ffs 178replaces the incorrect count in the 179summary information by the actual free-inode count. 180.NH 2 181Checking the inode state 182.PP 183An individual inode is not as likely to be corrupted as 184the allocation information. 185However, because of the great number of active inodes, 186a few of the inodes are usually corrupted. 187.PP | 176If the two counts do not agree, then 177.I fsck_ffs 178replaces the incorrect count in the 179summary information by the actual free-inode count. 180.NH 2 181Checking the inode state 182.PP 183An individual inode is not as likely to be corrupted as 184the allocation information. 185However, because of the great number of active inodes, 186a few of the inodes are usually corrupted. 187.PP |
| 188The list of inodes in the filesystem | 188The list of inodes in the file system |
| 189is checked sequentially starting with inode 2 190(inode 0 marks unused inodes; 191inode 1 is saved for future generations) | 189is checked sequentially starting with inode 2 190(inode 0 marks unused inodes; 191inode 1 is saved for future generations) |
| 192and progressing through the last inode in the filesystem. | 192and progressing through the last inode in the file system. |
| 193The state of each inode is checked for 194inconsistencies involving format and type, 195link count, 196duplicate blocks, 197bad blocks, 198and inode size. 199.PP 200Each inode contains a mode word. --- 12 unchanged lines hidden (view full) --- 213.NH 2 214Inode links 215.PP 216Each inode counts the 217total number of directory entries 218linked to the inode. 219.I Fsck_ffs 220verifies the link count of each inode | 193The state of each inode is checked for 194inconsistencies involving format and type, 195link count, 196duplicate blocks, 197bad blocks, 198and inode size. 199.PP 200Each inode contains a mode word. --- 12 unchanged lines hidden (view full) --- 213.NH 2 214Inode links 215.PP 216Each inode counts the 217total number of directory entries 218linked to the inode. 219.I Fsck_ffs 220verifies the link count of each inode |
| 221by starting at the root of the filesystem, | 221by starting at the root of the file system, |
| 222and descending through the directory structure. 223The actual link count for each inode 224is calculated during the descent. 225.PP 226If the stored link count is non-zero and the actual 227link count is zero, 228then no directory entry appears for the inode. 229If this happens, --- 44 unchanged lines hidden (view full) --- 274.I fsck_ffs 275prompts the operator to clear both inodes. 276The operator must decide which one should be kept 277and which one should be cleared. 278.PP 279.I Fsck_ffs 280checks the range of each block number claimed by an inode. 281If the block number is | 222and descending through the directory structure. 223The actual link count for each inode 224is calculated during the descent. 225.PP 226If the stored link count is non-zero and the actual 227link count is zero, 228then no directory entry appears for the inode. 229If this happens, --- 44 unchanged lines hidden (view full) --- 274.I fsck_ffs 275prompts the operator to clear both inodes. 276The operator must decide which one should be kept 277and which one should be cleared. 278.PP 279.I Fsck_ffs 280checks the range of each block number claimed by an inode. 281If the block number is |
| 282lower than the first data block in the filesystem, | 282lower than the first data block in the file system, |
| 283or greater than the last data block, 284then the block number is a 285.I "bad block number" . 286Many bad blocks in an inode are usually caused by | 283or greater than the last data block, 284then the block number is a 285.I "bad block number" . 286Many bad blocks in an inode are usually caused by |
| 287an indirect block that was not written to the filesystem, | 287an indirect block that was not written to the file system, |
| 288a condition which can only occur if there has been a hardware failure. 289If an inode contains bad block numbers, 290.I fsck_ffs 291prompts the operator to clear it. 292.NH 2 293Inode data size 294.PP 295Each inode contains a count of the number of data blocks --- 33 unchanged lines hidden (view full) --- 329.I Fsck_ffs 330can only check the validity of directory data blocks. 331.PP 332Each directory data block is checked for 333several types of inconsistencies. 334These inconsistencies include 335directory inode numbers pointing to unallocated inodes, 336directory inode numbers that are greater than | 288a condition which can only occur if there has been a hardware failure. 289If an inode contains bad block numbers, 290.I fsck_ffs 291prompts the operator to clear it. 292.NH 2 293Inode data size 294.PP 295Each inode contains a count of the number of data blocks --- 33 unchanged lines hidden (view full) --- 329.I Fsck_ffs 330can only check the validity of directory data blocks. 331.PP 332Each directory data block is checked for 333several types of inconsistencies. 334These inconsistencies include 335directory inode numbers pointing to unallocated inodes, 336directory inode numbers that are greater than |
| 337the number of inodes in the filesystem, | 337the number of inodes in the file system, |
| 338incorrect directory inode numbers for ``\fB.\fP'' and ``\fB..\fP'', | 338incorrect directory inode numbers for ``\fB.\fP'' and ``\fB..\fP'', |
| 339and directories that are not attached to the filesystem. | 339and directories that are not attached to the file system. |
| 340If the inode number in a directory data block 341references an unallocated inode, 342then 343.I fsck_ffs 344will remove that directory entry. 345Again, 346this condition can only arise when there has been a hardware failure. 347.PP --- 37 unchanged lines hidden (view full) --- 385If there are multiple hard links to a directory, 386the first one encountered is considered the real parent 387to which ``\fB..\fP'' should point; 388\fIfsck_ffs\fP recommends deletion for the subsequently discovered names. 389.NH 2 390File system connectivity 391.PP 392.I Fsck_ffs | 340If the inode number in a directory data block 341references an unallocated inode, 342then 343.I fsck_ffs 344will remove that directory entry. 345Again, 346this condition can only arise when there has been a hardware failure. 347.PP --- 37 unchanged lines hidden (view full) --- 385If there are multiple hard links to a directory, 386the first one encountered is considered the real parent 387to which ``\fB..\fP'' should point; 388\fIfsck_ffs\fP recommends deletion for the subsequently discovered names. 389.NH 2 390File system connectivity 391.PP 392.I Fsck_ffs |
| 393checks the general connectivity of the filesystem. 394If directories are not linked into the filesystem, then | 393checks the general connectivity of the file system. 394If directories are not linked into the file system, then |
| 395.I fsck_ffs | 395.I fsck_ffs |
| 396links the directory back into the filesystem in the | 396links the directory back into the file system in the |
| 397.I lost+found 398directory. 399This condition only occurs when there has been a hardware failure. 400.ds RH "References" 401.SH 402\s+2Acknowledgements\s0 403.PP 404I thank Bill Joy, Sam Leffler, Robert Elz and Dennis Ritchie | 397.I lost+found 398directory. 399This condition only occurs when there has been a hardware failure. 400.ds RH "References" 401.SH 402\s+2Acknowledgements\s0 403.PP 404I thank Bill Joy, Sam Leffler, Robert Elz and Dennis Ritchie |
| 405for their suggestions and help in implementing the new filesystem. | 405for their suggestions and help in implementing the new file system. |
| 406Thanks also to Robert Henry for his editorial input to 407get this document together. 408Finally we thank our sponsors, 409the National Science Foundation under grant MCS80-05144, 410and the Defense Advance Research Projects Agency (DoD) under 411Arpa Order No. 4031 monitored by Naval Electronic System Command under 412Contract No. N00039-82-C-0235. (Kirk McKusick, July 1983) 413.PP --- 40 unchanged lines hidden --- | 406Thanks also to Robert Henry for his editorial input to 407get this document together. 408Finally we thank our sponsors, 409the National Science Foundation under grant MCS80-05144, 410and the Defense Advance Research Projects Agency (DoD) under 411Arpa Order No. 4031 monitored by Naval Electronic System Command under 412Contract No. N00039-82-C-0235. (Kirk McKusick, July 1983) 413.PP --- 40 unchanged lines hidden --- |