diff options
Diffstat (limited to 'misc-utils/hardlink.1.adoc')
-rw-r--r-- | misc-utils/hardlink.1.adoc | 154 |
1 files changed, 154 insertions, 0 deletions
diff --git a/misc-utils/hardlink.1.adoc b/misc-utils/hardlink.1.adoc new file mode 100644 index 0000000..91d9867 --- /dev/null +++ b/misc-utils/hardlink.1.adoc @@ -0,0 +1,154 @@ +//po4a: entry man manual +//// +SPDX-License-Identifier: MIT + +Copyright (C) 2008 - 2012 Julian Andres Klode. See hardlink.c for license. +Copyright (C) 2021 Karel Zak <kzak@redhat.com> +//// += hardlink(1) +:doctype: manpage +:man manual: User Commands +:man source: util-linux {release-version} +:page-layout: base +:command: hardlink + +== NAME + +hardlink - link multiple copies of a file + +== SYNOPSIS + +*hardlink* [options] [_directory_|_file_]... + +== DESCRIPTION + +*hardlink* is a tool that replaces copies of a file with either hardlinks +or copy-on-write clones, thus saving space. + +*hardlink* first creates a binary tree of file sizes and then compares +the content of files that have the same size. There are two basic content +comparison methods. The *memcmp* method directly reads data blocks from +files and compares them. The other method is based on checksums (like SHA256); +in this case for each data block a checksum is calculated by the Linux kernel +crypto API, and this checksum is stored in userspace and used for file +comparisons. + +For each file also an "intro" buffer (32 bytes) is cached. This buffer is used +independently from the comparison method and requested cache-size and io-size. +The "intro" buffer dramatically reduces operations with data content as files +are very often different from the beginning. + +== OPTIONS + +include::man-common/help-version.adoc[] + +*-c*, *--content*:: +Consider only file content, not attributes, when determining whether two files are equal. Same as *-pot*. + +*-b*, *--io-size* _size_:: +The size of the *read*(2) or *sendfile*(2) buffer used when comparing file contents. +The _size_ argument may be followed by the multiplicative suffixes KiB, MiB, +etc. The "iB" is optional, e.g., "K" has the same meaning as "KiB". The +default is 8KiB for memcmp method and 1MiB for the other methods. The only +memcmp method uses process memory for the buffer, other methods use zero-copy +way and I/O operation is done in the kernel. The size may be altered on the fly +to fit a number of cached content checksums. + +*-d*, *--respect-dir*:: +Only try to link files with the same directory name. The top-level directory (as specified on the hardlink command line) is ignored. For example, *hardlink --respect-dir /foo /bar* will link _/foo/some/file_ with _/bar/some/file_, but not _/bar/other/file_. If combined with *--respect-name*, then entire paths (except the top-level directory) are compared. + +*-f*, *--respect-name*:: +Only try to link files with the same (base)name. It's strongly recommended to use long options rather than *-f* which is interpreted in a different way by other *hardlink* implementations. + +*-i*, *--include* _regex_:: +A regular expression to include files. If the option *--exclude* has been given, this option re-includes files which would otherwise be excluded. If the option is used without *--exclude*, only files matched by the pattern are included. + +*-m*, *--maximize*:: +Among equal files, keep the file with the highest link count. + +*-M*, *--minimize*:: +Among equal files, keep the file with the lowest link count. + +*-n*, *--dry-run*:: +Do not act, just print what would happen. + +*-o*, *--ignore-owner*:: +Link and compare files even if their owner information (user and group) differs. Results may be unpredictable. + +*-O*, *--keep-oldest*:: +Among equal files, keep the oldest file (least recent modification time). By default, the newest file is kept. If *--maximize* or *--minimize* is specified, the link count has a higher precedence than the time of modification. + +*-p*, *--ignore-mode*:: +Link and compare files even if their mode is different. Results may be slightly unpredictable. + +*-q*, *--quiet*:: +Quiet mode, don't print anything. + +*-r*, *--cache-size* _size_:: +The size of the cache for content checksums. All non-memcmp methods calculate checksum for each +file content block (see *--io-size*), these checksums are cached for the next comparison. The +size is important for large files or a large sets of files of the same size. The default is +10MiB. + +*-s*, *--minimum-size* _size_:: +The minimum size to consider. By default this is 1, so empty files will not be linked. The _size_ argument may be followed by the multiplicative suffixes KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g., "K" has the same meaning as "KiB"). + +*-S*, *--maximum-size* _size_:: +The maximum size to consider. By default this is 0 and 0 has the special meaning of unlimited. The _size_ argument may be followed by the multiplicative suffixes KiB (=1024), MiB (=1024*1024), and so on for GiB, TiB, PiB, EiB, ZiB and YiB (the "iB" is optional, e.g., "K" has the same meaning as "KiB"). + +*-t*, *--ignore-time*:: +Link and compare files even if their time of modification is different. This is usually a good choice. + +*-v*, *--verbose*:: +Verbose output, explain to the user what is being done. If specified once, every hardlinked file is displayed. If specified twice, it also shows every comparison. + +*-x*, *--exclude* _regex_:: +A regular expression which excludes files from being compared and linked. + +*-X*, *--respect-xattrs*:: +Only try to link files with the same extended attributes. + +*-y*, *--method* _name_:: +Set the file content comparison method. The currently supported methods are +sha256, sha1, crc32c and memcmp. The default is sha256, or memcmp if Linux +Crypto API is not available. The methods based on checksums are implemented in +zero-copy way, in this case file contents are not copied to the userspace and all +calculation is done in kernel. + +*--reflink*[=_when_]:: +Create copy-on-write clones (aka reflinks) rather than hardlinks. The reflinked files +share only on-disk data, but the file mode and owner can be different. It's recommended +to use it with *--ignore-owner* and *--ignore-mode* options. This option implies +*--skip-reflinks* to ignore already cloned files. ++ +The optional argument _when_ can be *never*, *always*, or *auto*. If the _when_ argument +is omitted, it defaults to *auto*, in this case, *hardlink* checks filesystem type and +uses reflinks on BTRFS and XFS only, and fallback to hardlinks when creating reflink is impossible. +The argument *always* disables filesystem type detection and fallback to hardlinks, in this case, +only reflinks are allowed. + +*--skip-reflinks*:: +Ignore already cloned files. This option may be used without *--reflink* when creating classic hardlinks. + + +== ARGUMENTS + +*hardlink* takes one or more directories which will be searched for files to be linked. + +== BUGS + +The original *hardlink* implementation uses the option *-f* to force hardlinks creation between filesystem. This very rarely usable feature is no more supported by the current *hardlink*. + +*hardlink* assumes that the trees it operates on do not change during operation. If a tree does change, the result is undefined and potentially dangerous. For example, if a regular file is replaced by a device, *hardlink* may start reading from the device. If a component of a path is replaced by a symbolic link or file permissions change, security may be compromised. Do not run *hardlink* on a changing tree or on a tree controlled by another user. + +== AUTHOR + +There are multiple *hardlink* implementations. The very first implementation is from Jakub Jelinek for Fedora distribution, this implementation has been used in util-linux between versions v2.34 to v2.36. The current implementations is based on Debian version from Julian Andres Klode. + +include::man-common/bugreports.adoc[] + +include::man-common/footer.adoc[] + +ifdef::translation[] +include::man-common/translation.adoc[] +endif::[] |