| 3.t (18808) | 3.t (66861) |
|---|---|
| 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 66861 2000-10-09 08:26:35Z adrian $ |
|
| 32.\" @(#)3.t 8.1 (Berkeley) 6/5/93 33.\" 34.ds RH Fixing corrupted file systems 35.NH 36Fixing corrupted file systems 37.PP 38A file system 39can become corrupted in several ways. --- 21 unchanged lines hidden (view full) --- 61Any piece of hardware can fail at any time. 62Failures 63can be as subtle as a bad block 64on a disk pack, or as blatant as a non-functional disk-controller. 65.NH 2 66Detecting and correcting corruption 67.PP 68Normally | 33.\" @(#)3.t 8.1 (Berkeley) 6/5/93 34.\" 35.ds RH Fixing corrupted file systems 36.NH 37Fixing corrupted file systems 38.PP 39A file system 40can become corrupted in several ways. --- 21 unchanged lines hidden (view full) --- 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 68.PP 69Normally |
| 69.I fsck | 70.I fsck_ffs |
| 70is run non-interactively. 71In this mode it will only fix 72corruptions that are expected to occur from an unclean halt. 73These actions are a proper subset of the actions that | 71is run non-interactively. 72In this mode it will only fix 73corruptions that are expected to occur from an unclean halt. 74These actions are a proper subset of the actions that |
| 74.I fsck | 75.I fsck_ffs |
| 75will take when it is running interactively. 76Throughout this paper we assume that | 76will take when it is running interactively. 77Throughout this paper we assume that |
| 77.I fsck | 78.I fsck_ffs |
| 78is being run interactively, 79and all possible errors can be encountered. 80When an inconsistency is discovered in this mode, | 79is being run interactively, 80and all possible errors can be encountered. 81When an inconsistency is discovered in this mode, |
| 81.I fsck | 82.I fsck_ffs |
| 82reports the inconsistency for the operator to 83chose a corrective action. 84.PP 85A quiescent\(dd 86.FS 87\(dd I.e., unmounted and not being written on. 88.FE 89file system may be checked for structural integrity 90by performing consistency checks on the 91redundant data intrinsic to a file system. 92The redundant data is either read from 93the file system, 94or computed from other known values. 95The file system 96.B must 97be in a quiescent state when | 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 90file system may be checked for structural integrity 91by performing consistency checks on the 92redundant data intrinsic to a file system. 93The redundant data is either read from 94the file system, 95or computed from other known values. 96The file system 97.B must 98be in a quiescent state when |
| 98.I fsck | 99.I fsck_ffs |
| 99is run, 100since | 100is run, 101since |
| 101.I fsck | 102.I fsck_ffs |
| 102is a multi-pass program. 103.PP 104In the following sections, 105we discuss methods to discover inconsistencies 106and possible corrective actions 107for the cylinder group blocks, the inodes, the indirect blocks, and 108the data blocks containing directory entries. 109.NH 2 --- 11 unchanged lines hidden (view full) --- 121The super-block is checked for inconsistencies 122involving file-system size, number of inodes, 123free-block count, and the free-inode count. 124The file-system size must be larger than the 125number of blocks used by the super-block 126and the number of blocks used by the list of inodes. 127The file-system size and layout information 128are the most critical pieces of information for | 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 --- 11 unchanged lines hidden (view full) --- 122The super-block is checked for inconsistencies 123involving file-system size, number of inodes, 124free-block count, and the free-inode count. 125The file-system size must be larger than the 126number of blocks used by the super-block 127and the number of blocks used by the list of inodes. 128The file-system size and layout information 129are the most critical pieces of information for |
| 129.I fsck . | 130.I fsck_ffs . |
| 130While there is no way to actually check these sizes, 131since they are statically determined by 132.I newfs , | 131While there is no way to actually check these sizes, 132since they are statically determined by 133.I newfs , |
| 133.I fsck | 134.I fsck_ffs |
| 134can check that these sizes are within reasonable bounds. 135All other file system checks require that these sizes be correct. 136If | 135can check that these sizes are within reasonable bounds. 136All other file system checks require that these sizes be correct. 137If |
| 137.I fsck | 138.I fsck_ffs |
| 138detects corruption in the static parameters of the default super-block, | 139detects corruption in the static parameters of the default super-block, |
| 139.I fsck | 140.I fsck_ffs |
| 140requests the operator to specify the location of an alternate super-block. 141.NH 2 142Free block checking 143.PP | 141requests the operator to specify the location of an alternate super-block. 142.NH 2 143Free block checking 144.PP |
| 144.I Fsck | 145.I Fsck_ffs |
| 145checks that all the blocks 146marked as free in the cylinder group block maps 147are not claimed by any files. 148When all the blocks have been initially accounted for, | 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, |
| 149.I fsck | 150.I fsck_ffs |
| 150checks that 151the number of free blocks 152plus the number of blocks claimed by the inodes 153equals the total number of blocks in the file system. 154.PP 155If anything is wrong with the block allocation maps, | 151checks that 152the number of free blocks 153plus the number of blocks claimed by the inodes 154equals the total number of blocks in the file system. 155.PP 156If anything is wrong with the block allocation maps, |
| 156.I fsck | 157.I fsck_ffs |
| 157will rebuild them, 158based on the list it has computed of allocated blocks. 159.PP 160The summary information associated with the super-block 161counts the total number of free blocks within the file system. | 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 file system. |
| 162.I Fsck | 163.I Fsck_ffs |
| 163compares this count to the 164number of free blocks it found within the file system. 165If the two counts do not agree, then | 164compares this count to the 165number of free blocks it found within the file system. 166If the two counts do not agree, then |
| 166.I fsck | 167.I fsck_ffs |
| 167replaces the incorrect count in the summary information 168by the actual free-block count. 169.PP 170The summary information 171counts the total number of free inodes within the file system. | 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 file system. |
| 172.I Fsck | 173.I Fsck_ffs |
| 173compares this count to the number 174of free inodes it found within the file system. 175If the two counts do not agree, then | 174compares this count to the number 175of free inodes it found within the file system. 176If the two counts do not agree, then |
| 176.I fsck | 177.I fsck_ffs |
| 177replaces the incorrect count in the 178summary information by the actual free-inode count. 179.NH 2 180Checking the inode state 181.PP 182An individual inode is not as likely to be corrupted as 183the allocation information. 184However, because of the great number of active inodes, --- 17 unchanged lines hidden (view full) --- 202regular inode, directory inode, symbolic link inode, 203special block inode, special character inode, or socket inode. 204Inodes may be found in one of three allocation states: 205unallocated, allocated, and neither unallocated nor allocated. 206This last state suggests an incorrectly formated inode. 207An inode can get in this state if 208bad data is written into the inode list. 209The only possible corrective action is for | 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, --- 17 unchanged lines hidden (view full) --- 203regular inode, directory inode, symbolic link inode, 204special block inode, special character inode, or socket inode. 205Inodes may be found in one of three allocation states: 206unallocated, allocated, and neither unallocated nor allocated. 207This last state suggests an incorrectly formated inode. 208An inode can get in this state if 209bad data is written into the inode list. 210The only possible corrective action is for |
| 210.I fsck | 211.I fsck_ffs |
| 211is to clear the inode. 212.NH 2 213Inode links 214.PP 215Each inode counts the 216total number of directory entries 217linked to the inode. | 212is to clear the inode. 213.NH 2 214Inode links 215.PP 216Each inode counts the 217total number of directory entries 218linked to the inode. |
| 218.I Fsck | 219.I Fsck_ffs |
| 219verifies the link count of each inode 220by starting at the root of the file system, 221and descending through the directory structure. 222The actual link count for each inode 223is calculated during the descent. 224.PP 225If the stored link count is non-zero and the actual 226link count is zero, 227then no directory entry appears for the inode. 228If this happens, | 220verifies the link count of each inode 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, |
| 229.I fsck | 230.I fsck_ffs |
| 230will place the disconnected file in the 231.I lost+found 232directory. 233If the stored and actual link counts are non-zero and unequal, 234a directory entry may have been added or removed without the inode being 235updated. 236If this happens, | 231will place the disconnected file in the 232.I lost+found 233directory. 234If the stored and actual link counts are non-zero and unequal, 235a directory entry may have been added or removed without the inode being 236updated. 237If this happens, |
| 237.I fsck | 238.I fsck_ffs |
| 238replaces the incorrect stored link count by the actual link count. 239.PP 240Each inode contains a list, 241or pointers to 242lists (indirect blocks), 243of all the blocks claimed by the inode. 244Since indirect blocks are owned by an inode, 245inconsistencies in indirect blocks directly 246affect the inode that owns it. 247.PP | 239replaces the incorrect stored link count by the actual link count. 240.PP 241Each inode contains a list, 242or pointers to 243lists (indirect blocks), 244of all the blocks claimed by the inode. 245Since indirect blocks are owned by an inode, 246inconsistencies in indirect blocks directly 247affect the inode that owns it. 248.PP |
| 248.I Fsck | 249.I Fsck_ffs |
| 249compares each block number claimed by an inode 250against a list of already allocated blocks. 251If another inode already claims a block number, 252then the block number is added to a list of 253.I "duplicate blocks" . 254Otherwise, the list of allocated blocks 255is updated to include the block number. 256.PP 257If there are any duplicate blocks, | 250compares each block number claimed by an inode 251against a list of already allocated blocks. 252If another inode already claims a block number, 253then the block number is added to a list of 254.I "duplicate blocks" . 255Otherwise, the list of allocated blocks 256is updated to include the block number. 257.PP 258If there are any duplicate blocks, |
| 258.I fsck | 259.I fsck_ffs |
| 259will perform a partial second 260pass over the inode list 261to find the inode of the duplicated block. 262The second pass is needed, 263since without examining the files associated with 264these inodes for correct content, 265not enough information is available 266to determine which inode is corrupted and should be cleared. 267If this condition does arise 268(only hardware failure will cause it), 269then the inode with the earliest 270modify time is usually incorrect, 271and should be cleared. 272If this happens, | 260will perform a partial second 261pass over the inode list 262to find the inode of the duplicated block. 263The second pass is needed, 264since without examining the files associated with 265these inodes for correct content, 266not enough information is available 267to determine which inode is corrupted and should be cleared. 268If this condition does arise 269(only hardware failure will cause it), 270then the inode with the earliest 271modify time is usually incorrect, 272and should be cleared. 273If this happens, |
| 273.I fsck | 274.I fsck_ffs |
| 274prompts the operator to clear both inodes. 275The operator must decide which one should be kept 276and which one should be cleared. 277.PP | 275prompts the operator to clear both inodes. 276The operator must decide which one should be kept 277and which one should be cleared. 278.PP |
| 278.I Fsck | 279.I Fsck_ffs |
| 279checks the range of each block number claimed by an inode. 280If the block number is 281lower than the first data block in the file system, 282or greater than the last data block, 283then the block number is a 284.I "bad block number" . 285Many bad blocks in an inode are usually caused by 286an indirect block that was not written to the file system, 287a condition which can only occur if there has been a hardware failure. 288If an inode contains bad block numbers, | 280checks the range of each block number claimed by an inode. 281If the block number is 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 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, |
| 289.I fsck | 290.I fsck_ffs |
| 290prompts the operator to clear it. 291.NH 2 292Inode data size 293.PP 294Each inode contains a count of the number of data blocks 295that it contains. 296The number of actual data blocks 297is the sum of the allocated data blocks 298and the indirect blocks. | 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 296that it contains. 297The number of actual data blocks 298is the sum of the allocated data blocks 299and the indirect blocks. |
| 299.I Fsck | 300.I Fsck_ffs |
| 300computes the actual number of data blocks 301and compares that block count against 302the actual number of blocks the inode claims. 303If an inode contains an incorrect count | 301computes the actual number of data blocks 302and compares that block count against 303the actual number of blocks the inode claims. 304If an inode contains an incorrect count |
| 304.I fsck | 305.I fsck_ffs |
| 305prompts the operator to fix it. 306.PP 307Each inode contains a thirty-two bit size field. 308The size is the number of data bytes 309in the file associated with the inode. 310The consistency of the byte size field is roughly checked 311by computing from the size field the maximum number of blocks 312that should be associated with the inode, --- 7 unchanged lines hidden (view full) --- 320All referenced blocks must be the same kind. 321The three types of data blocks are: 322plain data blocks, symbolic link data blocks, and directory data blocks. 323Plain data blocks 324contain the information stored in a file; 325symbolic link data blocks 326contain the path name stored in a link. 327Directory data blocks contain directory entries. | 306prompts the operator to fix it. 307.PP 308Each inode contains a thirty-two bit size field. 309The size is the number of data bytes 310in the file associated with the inode. 311The consistency of the byte size field is roughly checked 312by computing from the size field the maximum number of blocks 313that should be associated with the inode, --- 7 unchanged lines hidden (view full) --- 321All referenced blocks must be the same kind. 322The three types of data blocks are: 323plain data blocks, symbolic link data blocks, and directory data blocks. 324Plain data blocks 325contain the information stored in a file; 326symbolic link data blocks 327contain the path name stored in a link. 328Directory data blocks contain directory entries. |
| 328.I Fsck | 329.I Fsck_ffs |
| 329can only check the validity of directory data blocks. 330.PP 331Each directory data block is checked for 332several types of inconsistencies. 333These inconsistencies include 334directory inode numbers pointing to unallocated inodes, 335directory inode numbers that are greater than 336the number of inodes in the file system, 337incorrect directory inode numbers for ``\fB.\fP'' and ``\fB..\fP'', 338and directories that are not attached to the file system. 339If the inode number in a directory data block 340references an unallocated inode, 341then | 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 file system, 338incorrect directory inode numbers for ``\fB.\fP'' and ``\fB..\fP'', 339and directories that are not attached to the file system. 340If the inode number in a directory data block 341references an unallocated inode, 342then |
| 342.I fsck | 343.I fsck_ffs |
| 343will remove that directory entry. 344Again, 345this condition can only arise when there has been a hardware failure. 346.PP | 344will remove that directory entry. 345Again, 346this condition can only arise when there has been a hardware failure. 347.PP |
| 347.I Fsck | 348.I Fsck_ffs |
| 348also checks for directories with unallocated blocks (holes). 349Such directories should never be created. 350When found, | 349also checks for directories with unallocated blocks (holes). 350Such directories should never be created. 351When found, |
| 351.I fsck | 352.I fsck_ffs |
| 352will prompt the user to adjust the length of the offending directory 353which is done by shortening the size of the directory to the end of the 354last allocated block preceeding the hole. 355Unfortunately, this means that another Phase 1 run has to be done. | 353will prompt the user to adjust the length of the offending directory 354which is done by shortening the size of the directory to the end of the 355last allocated block preceeding the hole. 356Unfortunately, this means that another Phase 1 run has to be done. |
| 356.I Fsck 357will remind the user to rerun fsck after repairing a | 357.I Fsck_ffs 358will remind the user to rerun fsck_ffs after repairing a |
| 358directory containing an unallocated block. 359.PP 360If a directory entry inode number references 361outside the inode list, then | 359directory containing an unallocated block. 360.PP 361If a directory entry inode number references 362outside the inode list, then |
| 362.I fsck | 363.I fsck_ffs |
| 363will remove that directory entry. 364This condition occurs if bad data is written into a directory data block. 365.PP 366The directory inode number entry for ``\fB.\fP'' 367must be the first entry in the directory data block. 368The inode number for ``\fB.\fP'' 369must reference itself; 370e.g., it must equal the inode number 371for the directory data block. 372The directory inode number entry 373for ``\fB..\fP'' must be 374the second entry in the directory data block. 375Its value must equal the inode number for the 376parent of the directory entry 377(or the inode number of the directory 378data block if the directory is the 379root directory). 380If the directory inode numbers are 381incorrect, | 364will remove that directory entry. 365This condition occurs if bad data is written into a directory data block. 366.PP 367The directory inode number entry for ``\fB.\fP'' 368must be the first entry in the directory data block. 369The inode number for ``\fB.\fP'' 370must reference itself; 371e.g., it must equal the inode number 372for the directory data block. 373The directory inode number entry 374for ``\fB..\fP'' must be 375the second entry in the directory data block. 376Its value must equal the inode number for the 377parent of the directory entry 378(or the inode number of the directory 379data block if the directory is the 380root directory). 381If the directory inode numbers are 382incorrect, |
| 382.I fsck | 383.I fsck_ffs |
| 383will replace them with the correct values. 384If there are multiple hard links to a directory, 385the first one encountered is considered the real parent 386to which ``\fB..\fP'' should point; | 384will replace them with the correct values. 385If there are multiple hard links to a directory, 386the first one encountered is considered the real parent 387to which ``\fB..\fP'' should point; |
| 387\fIfsck\fP recommends deletion for the subsequently discovered names. | 388\fIfsck_ffs\fP recommends deletion for the subsequently discovered names. |
| 388.NH 2 389File system connectivity 390.PP | 389.NH 2 390File system connectivity 391.PP |
| 391.I Fsck | 392.I Fsck_ffs |
| 392checks the general connectivity of the file system. 393If directories are not linked into the file system, then | 393checks the general connectivity of the file system. 394If directories are not linked into the file system, then |
| 394.I fsck | 395.I fsck_ffs |
| 395links the directory back into the file system in the 396.I lost+found 397directory. 398This condition only occurs when there has been a hardware failure. 399.ds RH "References" 400.SH 401\s+2Acknowledgements\s0 402.PP --- 4 unchanged lines hidden (view full) --- 407Finally we thank our sponsors, 408the National Science Foundation under grant MCS80-05144, 409and the Defense Advance Research Projects Agency (DoD) under 410Arpa Order No. 4031 monitored by Naval Electronic System Command under 411Contract No. N00039-82-C-0235. (Kirk McKusick, July 1983) 412.PP 413I would like to thank Larry A. Wehr for advice that lead 414to the first version of | 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 --- 4 unchanged lines hidden (view full) --- 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 414I would like to thank Larry A. Wehr for advice that lead 415to the first version of |
| 415.I fsck | 416.I fsck_ffs |
| 416and Rick B. Brandt for adapting | 417and Rick B. Brandt for adapting |
| 417.I fsck | 418.I fsck_ffs |
| 418to 419UNIX/TS. (T. Kowalski, July 1979) 420.sp 2 421.SH 422\s+2References\s0 423.LP 424.IP [Dolotta78] 20 425Dolotta, T. A., and Olsson, S. B. eds., --- 17 unchanged lines hidden (view full) --- 443.B 57 , 4446 (July-August 1978, Part 2), pp. 1905-29. 445.IP [Thompson78] 20 446Thompson, K., 447UNIX Implementation, 448.I "The Bell System Technical Journal\^" 449.B 57 , 4506 (July-August 1978, Part 2), pp. 1931-46. | 419to 420UNIX/TS. (T. Kowalski, July 1979) 421.sp 2 422.SH 423\s+2References\s0 424.LP 425.IP [Dolotta78] 20 426Dolotta, T. A., and Olsson, S. B. eds., --- 17 unchanged lines hidden (view full) --- 444.B 57 , 4456 (July-August 1978, Part 2), pp. 1905-29. 446.IP [Thompson78] 20 447Thompson, K., 448UNIX Implementation, 449.I "The Bell System Technical Journal\^" 450.B 57 , 4516 (July-August 1978, Part 2), pp. 1931-46. |
| 451.ds RH Appendix A \- Fsck Error Conditions | 452.ds RH Appendix A \- Fsck_ffs Error Conditions |
| 452.bp | 453.bp |