1.\" Copyright (c) 2007 The DragonFly Project. All rights reserved. 2.\" 3.\" This code is derived from software contributed to The DragonFly Project 4.\" by Matthew Dillon <dillon@backplane.com> 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 10.\" 1. Redistributions of source code must retain the above copyright 11.\" notice, this list of conditions and the following disclaimer. 12.\" 2. Redistributions in binary form must reproduce the above copyright 13.\" notice, this list of conditions and the following disclaimer in 14.\" the documentation and/or other materials provided with the 15.\" distribution. 16.\" 3. Neither the name of The DragonFly Project nor the names of its 17.\" contributors may be used to endorse or promote products derived 18.\" from this software without specific, prior written permission. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 21.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 22.\" LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 23.\" FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 24.\" COPYRIGHT HOLDERS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 25.\" INCIDENTAL, SPECIAL, EXEMPLARY OR CONSEQUENTIAL DAMAGES (INCLUDING, 26.\" BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 27.\" LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED 28.\" AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, 29.\" OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT 30.\" OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31.\" SUCH DAMAGE. 32.\" 33.\" $DragonFly: src/sbin/hammer/hammer.8,v 1.58 2008/11/13 02:04:27 dillon Exp $ 34.\" 35.Dd February 12, 2010 36.Dt HAMMER 8 37.Os 38.Sh NAME 39.Nm hammer 40.Nd HAMMER file system utility 41.Sh SYNOPSIS 42.Nm 43.Fl h 44.Nm 45.Op Fl 2BqrvXy 46.Op Fl b Ar bandwidth 47.Op Fl c Ar cyclefile 48.Op Fl f Ar blkdevs 49.\" .Op Fl s Ar linkpath 50.Op Fl i Ar delay 51.Op Fl p Ar ssh-port 52.Op Fl t Ar seconds 53.Op Fl C Ar cachesize Ns Op Ns Cm \&: Ns Ar readahead 54.Op Fl S Ar splitsize 55.Ar command 56.Op Ar argument ... 57.Sh DESCRIPTION 58This manual page documents the 59.Nm 60utility which provides miscellaneous functions related to managing a 61.Nm HAMMER 62file system. 63For a general introduction to the 64.Nm HAMMER 65file system, its features, and 66examples on how to set up and maintain one, see 67.Xr HAMMER 5 . 68.Pp 69The options are as follows: 70.Bl -tag -width indent 71.It Fl h 72Get help. 73.It Fl 2 74Tell the mirror commands to use a 2-way protocol, which allows 75automatic negotiation of transaction id ranges. 76This option is automatically enabled by the 77.Cm mirror-copy 78command. 79.It Fl b Ar bandwidth 80Specify a bandwidth limit in bytes per second for mirroring streams. 81This option is typically used to prevent batch mirroring operations from 82loading down the machine. 83The bandwidth may be suffixed with 84.Cm k , m , 85or 86.Cm g 87to specify values in kilobytes, megabytes, and gigabytes per second. 88If no suffix is specified, bytes per second is assumed. 89.It Fl c Ar cyclefile 90When pruning and reblocking you can instruction 91.Nm 92to start at the object id stored in the specified file. 93If the file does not exist 94.Nm 95will start at the beginning. 96If 97.Nm 98is told to run for a 99specific period of time and is unable to complete the operation it will 100write out the current object id so the next run can pick up where it left off. 101If 102.Nm 103runs to completion it will delete 104.Ar cyclefile . 105.It Fl f Ar blkdevs 106Specify the volumes making up a 107.Nm HAMMER 108file system. 109.Ar Blkdevs 110is a colon-separated list of devices, each specifying a 111.Nm HAMMER 112volume. 113.It Fl i Ar delay 114When maintaining a streaming mirroring this option specifies the 115minimum delay after a batch ends before the next batch is allowed 116to start. 117The default is five seconds. 118.It Fl p Ar ssh-port 119This passes the -p <port> option to ssh when using a remote 120specification for the source and/or destination. 121.It Fl q 122Decrease verboseness. 123May be specified multiple times. 124.It Fl r 125Specify recursion for those commands which support it. 126.It Fl t Ar seconds 127When pruning and reblocking you can tell the utility to stop after a 128certain period of time. 129This option is used along with the 130.Fl c Ar cyclefile 131option to prune or reblock a portion of the file system incrementally. 132.It Fl v 133Increase verboseness. 134May be specified multiple times. 135.It Fl y 136Force "yes" for any interactive question. 137.It Fl B 138Bulk Transfer. 139.Cm Mirror-stream 140will not attempt to break-up large initial bulk transfers into smaller 141pieces. 142This can save time but if the link is lost in the middle of the 143initial bulk transfer you will have to start over from scratch. 144This option is not recommended. 145For more information see the 146.Fl S 147option. 148.It Fl C Ar cachesize Ns Op Ns Cm \&: Ns Ar readahead 149Set the memory cache size for any raw 150.Tn I/O . 151The default is 16m. 152A suffix of 153.Cm k 154for kilobytes and 155.Cm m 156for megabytes is allowed, 157else the cache size is specified in bytes. 158.Pp 159The read-behind/read-ahead defaults to 4 160.Nm HAMMER 161blocks. 162.Pp 163This option is typically only used with diagnostic commands 164as kernel-supported commands will use the kernel's buffer cache. 165.It Fl S Ar splitsize 166Specify the bulk splitup size in bytes for mirroring streams. 167When a mirror-stream is first started 168.Nm 169will do an initial run-through of the data to calculate good 170transaction ids to cut up the bulk transfers, creating 171restart points in case the stream is interrupted. 172If we don't do this and the stream is interrupted it might 173have to start all over again. 174The default is a splitsize of 100m. 175.Pp 176At the moment the run-through is disk-bandwidth-heavy but some 177future version will limit the run-through to just the B-Tree 178records and not the record data. 179.Pp 180The splitsize may be suffixed with 181.Cm k , m , 182or 183.Cm g 184to specify values in kilobytes, megabytes, or gigabytessecond. 185If no suffix is specified, bytes is assumed. 186.It Fl X 187Enable compression for any remote ssh specifications. Unfortunately 188the 189.Fl C 190option has already been reserved for other purposes so we had to use 191a different letter. This option is typically used with the 192mirroring directives. 193.El 194.Pp 195The commands are as follows: 196.Bl -tag -width indent 197.\" ==== synctid ==== 198.It Cm synctid Ar filesystem Op Cm quick 199Generates a guaranteed, formal 64 bit transaction id representing the 200current state of the specified 201.Nm HAMMER 202file system. 203The file system will be synced to the media. 204.Pp 205If the 206.Cm quick 207keyword is specified the file system will be soft-synced, meaning that a 208crash might still undo the state of the file system as of the transaction 209id returned but any new modifications will occur after the returned 210transaction id as expected. 211.Pp 212This operation does not create a snapshot. 213It is meant to be used 214to track temporary fine-grained changes to a subset of files and 215will only remain valid for 216.Ql @@ 217snapshot access purposes for the 218.Cm prune-min 219period configured for the PFS. 220If you desire a real snapshot then the 221.Cm snapq 222directive may be what you are looking for. 223.\" ==== bstats ==== 224.It Cm bstats Op Ar interval 225Output 226.Nm HAMMER 227B-tree statistics until interrupted. 228Pause 229.Ar interval 230seconds between each display. 231The default interval is one second. 232.\" ==== iostats ==== 233.It Cm iostats Op Ar interval 234Output 235.Nm HAMMER 236.Tn I/O 237statistics until interrupted. 238Pause 239.Ar interval 240seconds between each display. 241The default interval is one second. 242.\" ==== history ==== 243.It Cm history Ar path ... 244Show the modification history for 245.Nm HAMMER 246file's inode and data. 247.\" ==== blockmap ==== 248.It Cm blockmap 249Dump the blockmap for the file system. 250The 251.Nm HAMMER 252blockmap is two-layer 253blockmap representing the maximum possible file system size of 1 Exabyte. 254Needless to say the second layer is only present for blocks which exist. 255.Nm HAMMER Ns 's 256blockmap represents 8-Megabyte blocks, called big-blocks. 257Each big-block has an append 258point, a free byte count, and a typed zone id which allows content to be 259reverse engineered to some degree. 260.Pp 261In 262.Nm HAMMER 263allocations essentially appended to a selected big-block using 264the append offset and deducted from the free byte count. 265When space is freed the free byte count is adjusted but 266.Nm HAMMER 267does not track holes in big-blocks for reallocation. 268A big-block must be completely freed, either 269through normal file system operations or through reblocking, before 270it can be reused. 271.Pp 272Data blocks can be shared by deducting the space used from the free byte 273count for each shared references, though 274.Nm HAMMER 275does not yet make use of this feature. 276This means the free byte count can legally go negative. 277.Pp 278This command needs the 279.Fl f 280flag. 281.\" ==== show ==== 282.It Cm show Op Ar lo Ns Cm \&: Ns Ar objid 283Dump the B-tree. 284By default this command will validate all B-Tree 285linkages and CRCs, including data CRCs, and will report the most verbose 286information it can dig up. 287Any errors will show up with a 288.Ql B 289in column 1 along with various 290other error flags. 291.Pp 292If you specify a localization field or a localization:obj_id field, 293.Ar lo Ns Cm \&: Ns Ar objid , 294the dump will 295search for the key printing nodes as it recurses down, and then 296will iterate forwards. These fields are specified in HEX. 297Note that the pfsid is the top 16 bits of the 32 bit localization 298field so pfs #1 would be 00010000. 299.Pp 300If you use 301.Fl q 302the command will report less information about the inode contents. 303.Pp 304If you use 305.Fl qq 306the command will not report the content of the inode or other typed 307data at all. 308.Pp 309If you use 310.Fl qqq 311the command will not report volume header information, big-block fill 312ratios, mirror transaction ids, or report or check data CRCs. 313B-tree CRCs and linkages are still checked. 314.Pp 315This command needs the 316.Fl f 317flag. 318.\" ==== show-undo ==== 319.It Cm show-undo 320.Nm ( HAMMER 321VERSION 4+) 322Dump the UNDO map. 323.Pp 324This command needs the 325.Fl f 326flag. 327.\" .It Ar blockmap 328.\" Dump the B-tree, record, large-data, and small-data blockmaps, showing 329.\" physical block assignments and free space percentages. 330.\" ==== namekey1 ==== 331.It Cm namekey1 Ar filename 332Generate a 333.Nm HAMMER 33464 bit directory hash for the specified file name, using 335the original directory hash algorithm in version 1 of the file system. 336The low 32 bits are used as an iterator for hash collisions and will be 337output as 0. 338.\" ==== namekey2 ==== 339.It Cm namekey2 Ar filename 340Generate a 341.Nm HAMMER 34264 bit directory hash for the specified file name, using 343the new directory hash algorithm in version 2 of the file system. 344The low 32 bits are still used as an iterator but will start out containing 345part of the hash key. 346.\" ==== namekey32 ==== 347.It Cm namekey32 Ar filename 348Generate the top 32 bits of a 349.Nm HAMMER 35064 bit directory hash for the specified file name. 351.\" ==== info ==== 352.It Cm info 353Shows extended information about all the mounted 354.Nm HAMMER 355file systems. 356The information is divided into sections: 357.Bl -tag 358.It Volume identification 359General information, like the label of the 360.Nm HAMMER 361filesystem, the number of volumes it contains, the FSID, and the 362.Nm HAMMER 363version being used. 364.It Big block information 365Big block statistics, such as total, used, reserved and free big blocks. 366.It Space information 367Information about space used on the filesystem. 368Currently total size, used, reserved and free space are displayed. 369.It PFS Information 370Basic information about the PFSs currently present on a 371.Nm HAMMER 372filesystem. 373.Pp 374.Dq PFS ID 375is the ID of the PFS, with 0 being the root PFS. 376.Dq Snaps 377is the current snapshot count on the PFS. 378.Dq Mounted on 379displays the mount point of the PFS is currently mounted on (if any). 380.El 381.\" ==== cleanup ==== 382.It Cm cleanup Op Ar filesystem ... 383This is a meta-command which executes snapshot, prune, rebalance and reblock 384commands on the specified 385.Nm HAMMER 386file systems. 387If no 388.Ar filesystem 389is specified this command will clean-up all 390.Nm HAMMER 391file systems in use, including PFS's. 392To do this it will scan all 393.Nm HAMMER 394and 395.Nm null 396mounts, extract PFS id's, and clean-up each PFS found. 397.Pp 398This command will access a snapshots 399directory and a configuration file for each 400.Ar filesystem , 401creating them if necessary. 402.Bl -tag -width indent 403.It Nm HAMMER No version 2- 404The configuration file is 405.Pa config 406in the snapshots directory which defaults to 407.Pa <pfs>/snapshots . 408.It Nm HAMMER No version 3+ 409The configuration file is saved in file system meta-data, see 410.Nm 411.Cm config . 412The snapshots directory defaults to 413.Pa /var/hammer/<pfs> 414.Pa ( /var/hammer/root 415for root mount). 416.El 417.Pp 418The format of the configuration file is: 419.Bd -literal -offset indent 420snapshots <period> <retention-time> [any] 421prune <period> <max-runtime> 422rebalance <period> <max-runtime> 423reblock <period> <max-runtime> 424recopy <period> <max-runtime> 425.Ed 426.Pp 427Defaults are: 428.Bd -literal -offset indent 429snapshots 1d 60d # 0d 0d for PFS /tmp, /var/tmp, /usr/obj 430prune 1d 5m 431rebalance 1d 5m 432reblock 1d 5m 433recopy 30d 10m 434.Ed 435.Pp 436Time is given with a suffix of 437.Cm d , 438.Cm h , 439.Cm m 440or 441.Cm s 442meaning day, hour, minute and second. 443.Pp 444If the 445.Cm snapshots 446directive has a period of 0 and a retention time of 0 447then snapshot generation is disabled, removal of old snapshots are 448disabled, and prunes will use 449.Cm prune-everything . 450If the 451.Cm snapshots 452directive has a period of 0 but a non-zero retention time 453then this command will not create any new snapshots but will remove old 454snapshots it finds based on the retention time. 455.Pp 456By default only snapshots in the form 457.Ql snap- Ns Ar yyyymmdd Ns Op - Ns Ar HHMM 458are processed. 459If the 460.Cm any 461directive is specified as a third argument on the 462.Cm snapshots 463config line then any softlink of the form 464.Ql *- Ns Ar yyyymmdd Ns Op - Ns Ar HHMM 465or 466.Ql *. Ns Ar yyyymmdd Ns Op - Ns Ar HHMM 467will be processed. 468.Pp 469A prune max-runtime of 0 means unlimited. 470.Pp 471If period hasn't passed since the previous 472.Cm cleanup 473run nothing is done. 474For example a day has passed when midnight is passed (localtime). 475By default, 476.Dx 477is set up to run 478.Nm Ar cleanup 479nightly via 480.Xr periodic 8 . 481.Pp 482The default configuration file will create a daily snapshot, do a daily 483pruning, rebalancing and reblocking run and a monthly recopy run. 484Reblocking is defragmentation with a level of 95%, 485and recopy is full defragmentation. 486.Pp 487By default prune and rebalance operations are time limited to 5 minutes, 488reblock operations to a bit over 5 minutes, 489and recopy operations to a bit over 10 minutes. 490Reblocking and recopy runs are each broken down into four separate functions: 491btree, inodes, dirs and data. 492Each function is time limited to the time given in the configuration file, 493but the btree, inodes and dirs functions usually does not take very long time, 494full defragmentation is always used for these three functions. 495Also note that this directive will by default disable snapshots on 496the following PFS's: 497.Pa /tmp , 498.Pa /var/tmp 499and 500.Pa /usr/obj . 501.Pp 502The defaults may be adjusted by modifying the configuration file. 503The pruning and reblocking commands automatically maintain a cyclefile 504for incremental operation. 505If you interrupt (^C) the program the cyclefile will be updated, 506but a sub-command 507may continue to run in the background for a few seconds until the 508.Nm HAMMER 509ioctl detects the interrupt. 510The 511.Cm snapshots 512PFS option can be set to use another location for the snapshots directory. 513.Pp 514Work on this command is still in progress. 515Expected additions: 516An ability to remove snapshots dynamically as the 517file system becomes full. 518.\" ==== config ==== 519.It Cm config Op Ar filesystem Op Ar configfile 520.Nm ( HAMMER 521VERSION 3+) 522If zero or one arguments are specified this function dumps the current 523configuration file to stdout. 524Zero arguments specifies the PFS containing the current directory. 525This configuration file is stored in file system meta-data. 526If two arguments are specified this function installs a new config file. 527.Pp 528In 529.Nm HAMMER 530versions less than 3 the configuration file is by default stored in 531.Pa <pfs>/snapshots/config , 532but in all later versions the configuration file is stored in file system 533meta-data. 534.\" ==== viconfig ==== 535.It Cm viconfig Op Ar filesystem 536.Nm ( HAMMER 537VERSION 3+) 538Edit the configuration file and reinstall into file system meta-data when done. 539Zero arguments specifies the PFS containing the current directory. 540.\" ==== volume-add ==== 541.It Cm volume-add Ar device Ar filesystem 542This command will format 543.Ar device 544and add all of its space to 545.Ar filesystem . 546.Pp 547.Em NOTE! 548All existing data contained on 549.Ar device 550will be destroyed by this operation! 551If 552.Ar device 553contains a valid 554.Nm HAMMER 555file system, formatting will be denied. 556You can overcome this sanity check 557by using 558.Xr dd 1 559to erase the beginning sectors of the device. 560Also remember that you have to specify 561.Ar device , 562together with any other device that make up the file system, 563colon-separated to 564.Pa /etc/fstab 565and 566.Xr mount_hammer 8 . 567.\" ==== volume-del ==== 568.It Cm volume-del Ar device Ar filesystem 569This command will remove volume 570.Ar device 571from 572.Ar filesystem . 573.Pp 574Remember that you have to remove 575.Ar device 576from the colon-separated list in 577.Pa /etc/fstab 578and 579.Xr mount_hammer 8 . 580.\" ==== snapshot ==== 581.It Cm snapshot Oo Ar filesystem Oc Ar snapshot-dir 582.It Cm snapshot Ar filesystem Ar snapshot-dir Op Ar note 583Takes a snapshot of the file system either explicitly given by 584.Ar filesystem 585or implicitly derived from the 586.Ar snapshot-dir 587argument and creates a symlink in the directory provided by 588.Ar snapshot-dir 589pointing to the snapshot. 590If 591.Ar snapshot-dir 592is not a directory, it is assumed to be a format string passed to 593.Xr strftime 3 594with the current time as parameter. 595If 596.Ar snapshot-dir 597refers to an existing directory, a default format string of 598.Ql snap-%Y%d%m-%H%M 599is assumed and used as name for the newly created symlink. 600.Pp 601Snapshot is a per PFS operation, so a 602.Nm HAMMER 603file system and each PFS in it have to be snapshot separately. 604.Pp 605Example, assuming that 606.Pa /mysnapshots 607is on file system 608.Pa / 609and that 610.Pa /obj 611and 612.Pa /usr 613are file systems on their own, the following invocations: 614.Bd -literal -offset indent 615hammer snapshot /mysnapshots 616 617hammer snapshot /mysnapshots/%Y-%m-%d 618 619hammer snapshot /obj /mysnapshots/obj-%Y-%m-%d 620 621hammer snapshot /usr /my/snaps/usr "note" 622.Ed 623.Pp 624Would create symlinks similar to: 625.Bd -literal -offset indent 626/mysnapshots/snap-20080627-1210 -> /@@0x10d2cd05b7270d16 627 628/mysnapshots/2008-06-27 -> /@@0x10d2cd05b7270d16 629 630/mysnapshots/obj-2008-06-27 -> /obj@@0x10d2cd05b7270d16 631 632/my/snaps/usr/snap-20080627-1210 -> /usr@@0x10d2cd05b7270d16 633.Ed 634.Pp 635When run on a 636.Nm HAMMER 637version 3+ file system the snapshot is also recorded in file system meta-data 638along with the optional 639.Ar note . 640See the 641.Cm snapls 642directive. 643.\" ==== snap* ==== 644.It Cm snap Ar path Op Ar note 645.Nm ( HAMMER 646VERSION 3+) 647Create a snapshot for the PFS containing 648.Ar path 649and create a snapshot softlink. 650If the path specified is a 651directory a standard snapshot softlink will be created in the directory. 652The snapshot softlink points to the base of the mounted PFS. 653.It Cm snaplo Ar path Op Ar note 654.Nm ( HAMMER 655VERSION 3+) 656Create a snapshot for the PFS containing 657.Ar path 658and create a snapshot softlink. 659If the path specified is a 660directory a standard snapshot softlink will be created in the directory. 661The snapshot softlink points into the directory it is contained in. 662.It Cm snapq Ar dir Op Ar note 663.Nm ( HAMMER 664VERSION 3+) 665Create a snapshot for the PFS containing the specified directory but do 666not create a softlink. 667Instead output a path which can be used to access 668the directory via the snapshot. 669.Pp 670An absolute or relative path may be specified. 671The path will be used as-is as a prefix in the path output to stdout. 672As with the other 673snap and snapshot directives the snapshot transaction id will be registered 674in the file system meta-data. 675.It Cm snaprm Ar path Ar ... 676.It Cm snaprm Ar transid Ar ... 677.It Cm snaprm Ar filesystem Ar transid Ar ... 678.Nm ( HAMMER 679VERSION 3+) 680Remove a snapshot given its softlink or transaction id. 681If specifying a transaction id 682the snapshot is removed from file system meta-data but you are responsible 683for removing any related softlinks. 684.Pp 685If a softlink path is specified the filesystem and transaction id 686is derived from the contents of the softlink. 687If just a transaction id is specified it is assumed to be a snapshot 688in the HAMMER filesystem you are currently chdir'd into. 689You can also specify the filesystem and transaction id explicitly. 690.It Cm snapls Op Ar path ... 691.Nm ( HAMMER 692VERSION 3+) 693Dump the snapshot meta-data for PFSs containing each 694.Ar path 695listing all available snapshots and their notes. 696If no arguments are specified snapshots for the PFS containing the 697current directory are listed. 698This is the definitive list of snapshots for the file system. 699.\" ==== prune ==== 700.It Cm prune Ar softlink-dir 701Prune the file system based on previously created snapshot softlinks. 702Pruning is the act of deleting file system history. 703The 704.Cm prune 705command will delete file system history such that 706the file system state is retained for the given snapshots, 707and all history after the latest snapshot. 708By setting the per PFS parameter 709.Cm prune-min , 710history is guaranteed to be saved at least this time interval. 711All other history is deleted. 712.Pp 713The target directory is expected to contain softlinks pointing to 714snapshots of the file systems you wish to retain. 715The directory is scanned non-recursively and the mount points and 716transaction ids stored in the softlinks are extracted and sorted. 717The file system is then explicitly pruned according to what is found. 718Cleaning out portions of the file system is as simple as removing a 719snapshot softlink and then running the 720.Cm prune 721command. 722.Pp 723As a safety measure pruning only occurs if one or more softlinks are found 724containing the 725.Ql @@ 726snapshot id extension. 727Currently the scanned softlink directory must contain softlinks pointing 728to a single 729.Nm HAMMER 730mount. 731The softlinks may specify absolute or relative paths. 732Softlinks must use 20-character 733.Ql @@0x%016llx 734transaction ids, as might be returned from 735.Nm Cm synctid Ar filesystem . 736.Pp 737Pruning is a per PFS operation, so a 738.Nm HAMMER 739file system and each PFS in it have to be pruned separately. 740.Pp 741Note that pruning a file system may not immediately free-up space, 742though typically some space will be freed if a large number of records are 743pruned out. 744The file system must be reblocked to completely recover all available space. 745.Pp 746Example, lets say your that you didn't set 747.Cm prune-min , 748and snapshot directory contains the following links: 749.Bd -literal -offset indent 750lrwxr-xr-x 1 root wheel 29 May 31 17:57 snap1 -> 751/usr/obj/@@0x10d2cd05b7270d16 752 753lrwxr-xr-x 1 root wheel 29 May 31 17:58 snap2 -> 754/usr/obj/@@0x10d2cd13f3fde98f 755 756lrwxr-xr-x 1 root wheel 29 May 31 17:59 snap3 -> 757/usr/obj/@@0x10d2cd222adee364 758.Ed 759.Pp 760If you were to run the 761.Cm prune 762command on this directory, then the 763.Nm HAMMER 764.Pa /usr/obj 765mount will be pruned to retain the above three snapshots. 766In addition, history for modifications made to the file system older than 767the oldest snapshot will be destroyed and history for potentially fine-grained 768modifications made to the file system more recently than the most recent 769snapshot will be retained. 770.Pp 771If you then delete the 772.Pa snap2 773softlink and rerun the 774.Cm prune 775command, 776history for modifications pertaining to that snapshot would be destroyed. 777.Pp 778In 779.Nm HAMMER 780file system versions 3+ this command also scans the snapshots stored 781in the file system meta-data and includes them in the prune. 782.\" ==== prune-everything ==== 783.It Cm prune-everything Ar filesystem 784This command will remove all historical records from the file system. 785This directive is not normally used on a production system. 786.Pp 787This command does not remove snapshot softlinks but will delete all 788snapshots recorded in file system meta-data (for file system version 3+). 789The user is responsible for deleting any softlinks. 790.\" ==== rebalance ==== 791.It Cm rebalance Ar filesystem Op Ar saturation_percentage 792This command will rebalance the B-tree, nodes with small number of 793elements will be combined and element counts will be smoothed out 794between nodes. 795.Pp 796The saturation percentage is between 50% and 100%. 797The default is 75% (the 798.Sq % 799suffix is not needed). 800.\" ==== reblock* ==== 801.It Cm reblock Ar filesystem Op Ar fill_percentage 802.It Cm reblock-btree Ar filesystem Op Ar fill_percentage 803.It Cm reblock-inodes Ar filesystem Op Ar fill_percentage 804.It Cm reblock-dirs Ar filesystem Op Ar fill_percentage 805.It Cm reblock-data Ar filesystem Op Ar fill_percentage 806Attempt to defragment and free space for reuse by reblocking a live 807.Nm HAMMER 808file system. 809Big-blocks cannot be reused by 810.Nm HAMMER 811until they are completely free. 812This command also has the effect of reordering all elements, effectively 813defragmenting the file system. 814.Pp 815The default fill percentage is 100% and will cause the file system to be 816completely defragmented. 817All specified element types will be reallocated and rewritten. 818If you wish to quickly free up space instead try specifying 819a smaller fill percentage, such as 90% or 80% (the 820.Sq % 821suffix is not needed). 822.Pp 823Since this command may rewrite the entire contents of the disk it is 824best to do it incrementally from a 825.Xr cron 8 826job along with the 827.Fl c Ar cyclefile 828and 829.Fl t Ar seconds 830options to limit the run time. 831The file system would thus be defragmented over long period of time. 832.Pp 833It is recommended that separate invocations be used for each data type. 834B-tree nodes, inodes, and directories are typically the most important 835elements needing defragmentation. 836Data can be defragmented over a longer period of time. 837.Pp 838Reblocking is a per PFS operation, so a 839.Nm HAMMER 840file system and each PFS in it have to be reblocked separately. 841.\" ==== pfs-status ==== 842.It Cm pfs-status Ar dirpath ... 843Retrieve the mirroring configuration parameters for the specified 844.Nm HAMMER 845file systems or pseudo-filesystems (PFS's). 846.\" ==== pfs-master ==== 847.It Cm pfs-master Ar dirpath Op Ar options 848Create a pseudo-filesystem (PFS) inside a 849.Nm HAMMER 850file system. 851Up to 65535 such file systems can be created. 852Each PFS uses an independent inode numbering space making it suitable 853for use as a replication source or target. 854.Pp 855The 856.Cm pfs-master 857directive creates a PFS that you can read, write, and use as a mirroring 858source. 859.Pp 860It is recommended to use a 861.Nm null 862mount to access a PFS, for more information see 863.Xr HAMMER 5 . 864.\" ==== pfs-slave ==== 865.It Cm pfs-slave Ar dirpath Op Ar options 866Create a pseudo-filesystem (PFS) inside a 867.Nm HAMMER 868file system. 869Up to 65535 such file systems can be created. 870Each PFS uses an independent inode numbering space making it suitable 871for use as a replication source or target. 872.Pp 873The 874.Cm pfs-slave 875directive creates a PFS that you can use as a mirroring target. 876You will not be able to access a slave PFS until you have completed the 877first mirroring operation with it as the target (its root directory will 878not exist until then). 879.Pp 880Access to the pfs-slave via the special softlink, as described in the 881.Sx PFS NOTES 882below, allows 883.Nm HAMMER 884to 885dynamically modify the snapshot transaction id by returning a dynamic result 886from 887.Xr readlink 2 888calls. 889.Pp 890A PFS can only be truly destroyed with the 891.Cm pfs-destroy 892directive. 893Removing the softlink will not destroy the underlying PFS. 894.Pp 895It is recommended to use a 896.Nm null 897mount to access a PFS, for more information see 898.Xr HAMMER 5 . 899.\" ==== pfs-update ==== 900.It Cm pfs-update Ar dirpath Op Ar options 901Update the configuration parameters for an existing 902.Nm HAMMER 903file system or pseudo-filesystem. 904Options that may be specified: 905.Bl -tag -width indent 906.It Cm sync-beg-tid= Ns Ar 0x16llx 907This is the automatic snapshot access starting transaction id for 908mirroring slaves. 909This parameter is normally updated automatically by the 910.Cm mirror-write 911directive. 912.Pp 913It is important to note that accessing a mirroring slave 914with a transaction id greater than the last fully synchronized transaction 915id can result in an unreliable snapshot since you will be accessing 916data that is still undergoing synchronization. 917.Pp 918Manually modifying this field is dangerous and can result in a broken mirror. 919.It Cm sync-end-tid= Ns Ar 0x16llx 920This is the current synchronization point for mirroring slaves. 921This parameter is normally updated automatically by the 922.Cm mirror-write 923directive. 924.Pp 925Manually modifying this field is dangerous and can result in a broken mirror. 926.It Cm shared-uuid= Ns Ar uuid 927Set the shared UUID for this file system. 928All mirrors must have the same shared UUID. 929For safety purposes the 930.Cm mirror-write 931directives will refuse to operate on a target with a different shared UUID. 932.Pp 933Changing the shared UUID on an existing, non-empty mirroring target, 934including an empty but not completely pruned target, 935can lead to corruption of the mirroring target. 936.It Cm unique-uuid= Ns Ar uuid 937Set the unique UUID for this file system. 938This UUID should not be used anywhere else, 939even on exact copies of the file system. 940.It Cm label= Ns Ar string 941Set a descriptive label for this file system. 942.It Cm snapshots= Ns Ar string 943Specify the snapshots directory which 944.Nm 945.Cm cleanup 946will use to manage this PFS. 947.Bl -tag -width indent 948.It Nm HAMMER No version 2- 949The snapshots directory does not need to be configured for 950PFS masters and will default to 951.Pa <pfs>/snapshots . 952.Pp 953PFS slaves are mirroring slaves so you cannot configure a snapshots 954directory on the slave itself to be managed by the slave's machine. 955In fact, the slave will likely have a 956.Pa snapshots 957sub-directory mirrored 958from the master, but that directory contains the configuration the master 959is using for its copy of the file system, not the configuration that we 960want to use for our slave. 961.Pp 962It is recommended that 963.Pa <fs>/var/slaves/<name> 964be configured for a PFS slave, where 965.Pa <fs> 966is the base 967.Nm HAMMER 968file system, and 969.Pa <name> 970is an appropriate label. 971.It Nm HAMMER No version 3+ 972The snapshots directory does not need to be configured for PFS masters or 973slaves. 974The snapshots directory defaults to 975.Pa /var/hammer/<pfs> 976.Pa ( /var/hammer/root 977for root mount). 978.El 979.Pp 980You can control snapshot retention on your slave independent of the master. 981.It Cm snapshots-clear 982Zero out the 983.Cm snapshots 984directory path for this PFS. 985.It Cm prune-min= Ns Ar N Ns Cm d 986.It Cm prune-min= Ns Oo Ar N Ns Cm d/ Oc Ns \ 987Ar hh Ns Op Cm \&: Ns Ar mm Ns Op Cm \&: Ns Ar ss 988Set the minimum fine-grained data retention period. 989.Nm HAMMER 990always retains fine-grained history up to the most recent snapshot. 991You can extend the retention period further by specifying a non-zero 992pruning minimum. 993Any snapshot softlinks within the retention period are ignored 994for the purposes of pruning (the fine grained history is retained). 995Number of days, hours, minutes and seconds are given as 996.Ar N , hh , mm 997and 998.Ar ss . 999.Pp 1000Because the transaction id in the snapshot softlink cannot be used 1001to calculate a timestamp, 1002.Nm HAMMER 1003uses the earlier of the 1004.Fa st_ctime 1005or 1006.Fa st_mtime 1007field of the softlink to 1008determine which snapshots fall within the retention period. 1009Users must be sure to retain one of these two fields when manipulating 1010the softlink. 1011.El 1012.\" ==== pfs-upgrade ==== 1013.It Cm pfs-upgrade Ar dirpath 1014Upgrade a PFS from slave to master operation. 1015The PFS will be rolled back to the current end synchronization transaction id 1016(removing any partial synchronizations), and will then become writable. 1017.Pp 1018.Em WARNING! 1019.Nm HAMMER 1020currently supports only single masters and using 1021this command can easily result in file system corruption 1022if you don't know what you are doing. 1023.Pp 1024This directive will refuse to run if any programs have open descriptors 1025in the PFS, including programs chdir'd into the PFS. 1026.\" ==== pfs-downgrade ==== 1027.It Cm pfs-downgrade Ar dirpath 1028Downgrade a master PFS from master to slave operation 1029The PFS becomes read-only and access will be locked to its 1030.Cm sync-end-tid . 1031.Pp 1032This directive will refuse to run if any programs have open descriptors 1033in the PFS, including programs chdir'd into the PFS. 1034.\" ==== pfs-destroy ==== 1035.It Cm pfs-destroy Ar dirpath 1036This permanently destroys a PFS. 1037.Pp 1038This directive will refuse to run if any programs have open descriptors 1039in the PFS, including programs chdir'd into the PFS. 1040.\" ==== mirror-read ==== 1041.It Cm mirror-read Ar filesystem Op Ar begin-tid 1042Generate a mirroring stream to stdout. 1043The stream ends when the transaction id space has been exhausted. 1044.\" ==== mirror-read-stream ==== 1045.It Cm mirror-read-stream Ar filesystem Op Ar begin-tid 1046Generate a mirroring stream to stdout. 1047Upon completion the stream is paused until new data is synced to the 1048master, then resumed. 1049Operation continues until the pipe is broken. 1050.\" ==== mirror-write ==== 1051.It Cm mirror-write Ar filesystem 1052Take a mirroring stream on stdin. 1053.Pp 1054This command will fail if the 1055.Cm shared-uuid 1056configuration field for the two file systems do not match. 1057.Pp 1058If the target PFS does not exist this command will ask you whether 1059you want to create a compatible PFS slave for the target or not. 1060.\" ==== mirror-dump ==== 1061.It Cm mirror-dump 1062A 1063.Cm mirror-read 1064can be piped into a 1065.Cm mirror-dump 1066to dump an ASCII representation of the mirroring stream. 1067.\" ==== mirror-copy ==== 1068.\".It Cm mirror-copy Ar [[user@]host:]filesystem [[user@]host:]filesystem 1069.It Cm mirror-copy \ 1070Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem \ 1071Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem 1072This is a shortcut which pipes a 1073.Cm mirror-read 1074command to a 1075.Cm mirror-write 1076command. 1077If a remote host specification is made the program forks a 1078.Xr ssh 1 1079and execs the 1080.Cm mirror-read 1081and/or 1082.Cm mirror-write 1083on the appropriate host. 1084The source may be a master or slave PFS, and the target must be a slave PFS. 1085.Pp 1086This command also established full duplex communication and turns on 1087the two-way protocol feature which automatically negotiates transaction id 1088ranges without having to use a cyclefile. 1089If the operation completes successfully the target PFS's 1090.Cm sync-end-tid 1091will be updated. 1092Note that you must re-chdir into the target PFS to see the updated information. 1093If you do not you will still be in the previous snapshot. 1094.Pp 1095If the target PFS does not exist this command will ask you whether 1096you want to create a compatible PFS slave for the target or not. 1097.\" ==== mirror-stream ==== 1098.\".It Cm mirror-stream Ar [[user@]host:]filesystem [[user@]host:]filesystem 1099.It Cm mirror-stream \ 1100Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem \ 1101Oo Oo Ar user Ns Cm @ Oc Ns Ar host Ns Cm \&: Oc Ns Ar filesystem 1102This command works similarly to 1103.Cm mirror-copy 1104but does not exit after the initial mirroring completes. 1105The mirroring operation will resume as changes continue to be made to the 1106master. 1107The command is commonly used with 1108.Fl i Ar delay 1109and 1110.Fl b Ar bandwidth 1111options to keep the mirroring target in sync with the source on a continuing 1112basis. 1113.Pp 1114If the pipe is broken the command will automatically retry after sleeping 1115for a short while. 1116The time slept will be 15 seconds plus the time given in the 1117.Fl i 1118option. 1119.Pp 1120This command also detects the initial-mirroring case and spends some 1121time scanning the B-Tree to find good break points, allowing the initial 1122bulk mirroring operation to be broken down into about 20 separate pieces. 1123This means that the user can kill and restart the operation and it will 1124not have to start from scratch once it has gotten past the first chunk. 1125The 1126.Fl B 1127option may be used to disable this feature and perform an initial bulk 1128transfer instead. 1129.\" ==== version ==== 1130.It Cm version Ar filesystem 1131This command returns the 1132.Nm HAMMER 1133file system version for the specified 1134.Ar filesystem 1135as well as the range of versions supported in the kernel. 1136The 1137.Fl q 1138option may be used to remove the summary at the end. 1139.\" ==== version-upgrade ==== 1140.It Cm version-upgrade Ar filesystem Ar version Op Cm force 1141This command upgrades the 1142.Nm HAMMER 1143.Ar filesystem 1144to the specified 1145.Ar version . 1146Once upgraded a file system may not be downgraded. 1147If you wish to upgrade a file system to a version greater or equal to the 1148work-in-progress version number you must specify the 1149.Cm force 1150directive. 1151Use of WIP versions should be relegated to testing and may require wiping 1152the file system as development progresses, even though the WIP version might 1153not change. 1154.Pp 1155.Em NOTE! 1156This command operates on the entire 1157.Nm HAMMER 1158file system and is not a per PFS operation. 1159All PFS's will be affected. 1160.Bl -tag -width indent 1161.It 1 1162.Dx 2.0 1163default version, first 1164.Nm HAMMER 1165release. 1166.It 2 1167.Dx 2.3 . 1168New directory entry layout. 1169This version is using a new directory hash key. 1170.It 3 1171.Dx 2.5 . 1172New snapshot management, using file system meta-data for saving 1173configuration file and snapshots (transaction ids etc.). 1174Also default snapshots directory has changed. 1175.It 4 1176.Dx 2.5 1177default version. 1178New undo/flush, giving faster sync. 1179.El 1180.El 1181.\".Sh EXAMPLES 1182.Sh ENVIRONMENT 1183If the following environment variables exist, they will be used by 1184.Nm : 1185.Bl -tag -width ".Ev EDITOR" 1186.It Ev EDITOR 1187The editor program specified in the variable 1188.Ev EDITOR 1189will be invoked instead of the default editor, which is 1190.Xr vi 1 1191.It Ev VISUAL 1192Same effect as 1193.Ev EDITOR 1194variable. 1195.El 1196.Sh PSEUDO-FILESYSTEM (PFS) NOTES 1197The root of a PFS is not hooked into the primary 1198.Nm HAMMER 1199file system as a directory. 1200Instead, 1201.Nm HAMMER 1202creates a special softlink called 1203.Ql @@PFS%05d 1204(exactly 10 characters long) in the primary 1205.Nm HAMMER 1206file system. 1207.Nm HAMMER 1208then modifies the contents of the softlink as read by 1209.Xr readlink 2 , 1210and thus what you see with an 1211.Nm ls 1212command or if you were to 1213.Nm cd 1214into the link. 1215If the PFS is a master the link reflects the current state of the PFS. 1216If the PFS is a slave the link reflects the last completed snapshot, and the 1217contents of the link will change when the next snapshot is completed, and 1218so forth. 1219.Pp 1220The 1221.Nm 1222utility employs numerous safeties to reduce user foot-shooting. 1223The 1224.Cm mirror-copy 1225directive requires that the target be configured as a slave and that the 1226.Cm shared-uuid 1227field of the mirroring source and target match. 1228.Sh UPGRADE INSTRUCTIONS HAMMER V1 TO V2 1229This upgrade changes the way directory entries are stored. 1230It is possible to upgrade a V1 file system to V2 in place, but 1231directories created prior to the upgrade will continue to use 1232the old layout. 1233.Pp 1234Note that the slave mirroring code in the target kernel had bugs in 1235V1 which can create an incompatible root directory on the slave. 1236Do not mix a 1237.Nm HAMMER 1238master created after the upgrade with a 1239.Nm HAMMER 1240slave created prior to the upgrade. 1241.Pp 1242Any directories created after upgrading will use a new layout. 1243.Sh UPGRADE INSTRUCTIONS HAMMER V2 TO V3 1244This upgrade adds meta-data elements to the B-Tree. 1245It is possible to upgrade a V2 file system to V3 in place. 1246After issuing the upgrade be sure to run a 1247.Nm 1248.Cm cleanup 1249to perform post-upgrade tasks. 1250.Pp 1251After making this upgrade running a 1252.Nm 1253.Cm cleanup 1254will move the 1255.Pa <pfs>/snapshots 1256directory for each PFS mount into 1257.Pa /var/hammer/<pfs> . 1258A 1259.Nm HAMMER 1260root mount will migrate 1261.Pa /snapshots 1262into 1263.Pa /var/hammer/root . 1264Migration occurs only once and only if you have not specified 1265a snapshots directory in the PFS configuration. 1266If you have specified a snapshots directory in the PFS configuration no 1267automatic migration will occur. 1268.Pp 1269For slaves, if you desire, you can migrate your snapshots 1270config to the new location manually and then clear the 1271snapshot directory configuration in the slave PFS. 1272The new snapshots hierarchy is designed to work with 1273both master and slave PFSs equally well. 1274.Pp 1275In addition, the old config file will be moved to file system meta-data, 1276editable via the new 1277.Nm 1278.Cm viconfig 1279directive. 1280The old config file will be deleted. 1281Migration occurs only once. 1282.Pp 1283The V3 file system has new 1284.Cm snap* 1285directives for creating snapshots. 1286All snapshot directives, including the original, will create 1287meta-data entries for the snapshots and the pruning code will 1288automatically incorporate these entries into its list and 1289expire them the same way it expires softlinks. 1290If you by accident blow away your snapshot softlinks you can use the 1291.Cm snapls 1292directive to get a definitive list from the file system meta-data and 1293regenerate them from that list. 1294.Pp 1295.Em WARNING! 1296If you are using 1297.Nm 1298to backup file systems your scripts may be using the 1299.Cm synctid 1300directive to generate transaction ids. 1301This directive does not create a snapshot. 1302You will have to modify your scripts to use the 1303.Cm snapq 1304directive to generate the linkbuf for the softlink you create, or 1305use one of the other 1306.Cm snap* 1307directives. 1308The older 1309.Cm snapshot 1310directive will continue to work as expected and in V3 it will also 1311record the snapshot transaction id in file system meta-data. 1312You may also want to make use of the new 1313.Ar note 1314tag for the meta-data. 1315.Pp 1316.Em WARNING! 1317If you used to remove snapshot softlinks with 1318.Nm rm 1319you should probably start using the 1320.Cm snaprm 1321directive instead to also remove the related meta-data. 1322The pruning code scans the meta-data so just removing the 1323softlink is not sufficient. 1324.Sh UPGRADE INSTRUCTIONS HAMMER V3 TO V4 1325This upgrade changes undo/flush, giving faster sync. 1326It is possible to upgrade a V3 file system to V4 in place. 1327This upgrade reformats the UNDO FIFO (typically 1GB), so upgrade might take 1328a minute or two depending. 1329.Pp 1330Version 4 allows the UNDO FIFO to be flushed without also having 1331to flush the volume header, removing 2 of the 4 disk syncs typically 1332required for an fsync() and removing 1 of the 2 disk syncs typically 1333required for a flush sequence. 1334.Sh FSYNC FLUSH MODES 1335Hammer implements five different fsync flush modes via the 1336.Li vfs.hammer.fsync_mode 1337sysctl. 1338.Pp 1339.Bl -tag -width indent 1340.It mode 0 1341Full synchronous fsync semantics without REDO. 1342.Pp 1343Hammer will not generate REDOs. A fsync() will completely sync 1344the data and meta-data and double-flush the FIFO, including 1345issuing two disk synchronization commands. The data is guaranteed 1346to be on the media as of when fsync() returns. 1347Needless to say, this is slow. 1348.Pp 1349Even though all modes are available in that release the REDO 1350semantics are not well tested yet and not enabled by default. 1351.It mode 1 1352Relaxed asynchronous fsync semantics without REDO. 1353.Pp 1354This mode works the same as mode 0 except the last disk synchronization 1355command is not issued. It is faster than mode 0 but not even remotely 1356close to the speed you get with mode 2 or mode 3. 1357.Pp 1358Note that there is no chance of meta-data corruption when using this 1359mode, it simply means that the data you wrote and then fsync()'d might 1360not have made it to the media if the storage system crashes at a bad 1361time. 1362.Pp 1363.It mode 2 1364Full synchronous fsync semantics using REDO. 1365.Pp 1366Hammer will generate REDOs in the UNDO/REDO FIFO based on a heuristic. 1367If this is sufficient to satisfy the fsync() operation the blocks 1368will be written out and hammer will wait for the I/Os to complete, 1369and then followup with a disk sync command to guarantee the data 1370is on the media before returning. 1371This is slower than mode 3 and can result in significant disk or 1372SSDs overheads, though not as bad as mode 0 or mode 1. 1373.Pp 1374.It mode 3 1375Relaxed asynchronous fsync semantics using REDO. 1376.Pp 1377Hammer will generate REDOs in the UNDO/REDO FIFO based on a heuristic. 1378If this is sufficient to satisfy the fsync() operation the blocks 1379will be written out and hammer will wait for the I/Os to complete, 1380but will 1381.Em NOT 1382issue a disk synchronization command. 1383.Pp 1384Note that there is no chance of meta-data corruption when using this 1385mode, it simply means that the data you wrote and then fsync()'d might 1386not have made it to the media if the storage system crashes at a bad 1387time. 1388.Pp 1389This mode is the fastest production fsyncing mode available. 1390This mode is equivalent to how the UFS fsync in the BSDs operates. 1391.Pp 1392.It mode 4 1393fsync is ignored. 1394.Pp 1395Calls to fsync() will be ignored. This mode is primarily designed 1396for testing and should not be used on a production system. 1397.El 1398.Sh FILES 1399.Bl -tag -width ".It Pa <fs>/var/slaves/<name>" -compact 1400.It Pa <pfs>/snapshots 1401default per PFS snapshots directory 1402.Nm ( HAMMER 1403VERSION 2-) 1404.It Pa /var/hammer/<pfs> 1405default per PFS snapshots directory (not root) 1406.Nm ( HAMMER 1407VERSION 3+) 1408.It Pa /var/hammer/root 1409default snapshots directory for root directory 1410.Nm ( HAMMER 1411VERSION 3+) 1412.It Pa <snapshots>/config 1413per PFS 1414.Nm 1415.Cm cleanup 1416configuration file 1417.Nm ( HAMMER 1418VERSION 2-) 1419.It Pa <fs>/var/slaves/<name> 1420recommended slave PFS snapshots directory 1421.Nm ( HAMMER 1422VERSION 2-) 1423.El 1424.Sh EXIT STATUS 1425.Ex -std 1426.Sh SEE ALSO 1427.Xr ssh 1 , 1428.Xr undo 1 , 1429.Xr HAMMER 5 , 1430.Xr periodic.conf 5 , 1431.Xr mount_hammer 8 , 1432.Xr mount_null 8 , 1433.Xr newfs_hammer 8 1434.Sh HISTORY 1435The 1436.Nm 1437utility first appeared in 1438.Dx 1.11 . 1439.Sh AUTHORS 1440.An Matthew Dillon Aq dillon@backplane.com 1441