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295b3979 | 1 | //po4a: entry man manual |
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2 | //// |
3 | SPDX-License-Identifier: MIT | |
4 | ||
5 | Copyright (C) 2008 - 2012 Julian Andres Klode. See hardlink.c for license. | |
6 | Copyright (C) 2021 Karel Zak <kzak@redhat.com> | |
7 | //// | |
8 | = hardlink(1) | |
9 | :doctype: manpage | |
10 | :man manual: User Commands | |
11 | :man source: util-linux {release-version} | |
12 | :page-layout: base | |
13 | :command: hardlink | |
14 | ||
15 | == NAME | |
16 | ||
17 | hardlink - link multiple copies of a file | |
18 | ||
19 | == SYNOPSIS | |
20 | ||
21 | *hardlink* [options] [_directory_|_file_]... | |
22 | ||
23 | == DESCRIPTION | |
24 | ||
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25 | *hardlink* is a tool that replaces copies of a file with either hardlinks |
26 | or copy-on-write clones, thus saving space. | |
27 | ||
28 | *hardlink* first creates a binary tree of file sizes and then compares | |
29 | the content of files that have the same size. There are two basic content | |
30 | comparison methods. The *memcmp* method directly reads data blocks from | |
31 | files and compares them. The other method is based on checksums (like SHA256); | |
32 | in this case for each data block a checksum is calculated by the Linux kernel | |
33 | crypto API, and this checksum is stored in userspace and used for file | |
34 | comparisons. | |
35 | ||
36 | For each file also an "intro" buffer (32 bytes) is cached. This buffer is used | |
37 | independently from the comparison method and requested cache-size and io-size. | |
38 | The "intro" buffer dramatically reduces operations with data content as files | |
39 | are very often different from the beginning. | |
f3212b91 | 40 | |
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41 | == OPTIONS |
42 | ||
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43 | include::man-common/help-version.adoc[] |
44 | If specified once, every hardlinked file is displayed, if specified twice, it also shows every comparison. | |
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45 | |
46 | *-q*, *--quiet*:: | |
2c646c80 | 47 | Quiet mode, don't print anything. |
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48 | |
49 | *-n*, *--dry-run*:: | |
2c646c80 | 50 | Do not act, just print what would happen. |
6c64d12d | 51 | |
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52 | *-y*, *--method* _name_:: |
53 | Set the file content comparison method. The currently supported methods are | |
344b0cd4 | 54 | sha256, sha1, crc32c and memcmp. The default is sha256, or memcmp if Linux |
259bed15 | 55 | Crypto API is not available. The methods based on checksums are implemented in |
344b0cd4 | 56 | zero-copy way, in this case file contents are not copied to the userspace and all |
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57 | calculation is done in kernel. |
58 | ||
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59 | *--reflink*[=_when_]:: |
60 | Create copy-on-write clones (aka reflinks) rather than hardlinks. The reflinked files | |
61 | share only on-disk data, but the file mode and owner can be different. It's recommended | |
62 | to use it with *--ignore-owner* and *--ignore-mode* options. This option implies | |
63 | *--skip-reflinks* to ignore already cloned files. | |
64 | + | |
65 | The optional argument _when_ can be *never*, *always*, or *auto*. If the _when_ argument | |
344b0cd4 | 66 | is omitted, it defaults to *auto*, in this case, *hardlink* checks filesystem type and |
66a38e97 | 67 | uses reflinks on BTRFS and XFS only, and fallback to hardlinks when creating reflink is impossible. |
344b0cd4 | 68 | The argument *always* disables filesystem type detection and fallback to hardlinks, in this case, |
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69 | only reflinks are allowed. |
70 | ||
71 | *--skip-reflinks*:: | |
72 | Ignore already cloned files. This option may be used without *--reflink* when creating classic hardlinks. | |
73 | ||
6c64d12d | 74 | *-f*, *--respect-name*:: |
145d42e9 | 75 | 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. |
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76 | |
77 | *-p*, *--ignore-mode*:: | |
145d42e9 | 78 | Link and compare files even if their mode is different. Results may be slightly unpredictable. |
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79 | |
80 | *-o*, *--ignore-owner*:: | |
145d42e9 | 81 | Link and compare files even if their owner information (user and group) differs. Results may be unpredictable. |
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82 | |
83 | *-t*, *--ignore-time*:: | |
145d42e9 | 84 | Link and compare files even if their time of modification is different. This is usually a good choice. |
6c64d12d | 85 | |
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86 | *-c* *--content*:: |
87 | Consider only file content, not attributes, when determining whether two files are equal. Same as *-pot*. | |
88 | ||
6c64d12d | 89 | *-X*, *--respect-xattrs*:: |
2c646c80 | 90 | Only try to link files with the same extended attributes. |
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91 | |
92 | *-m*, *--maximize*:: | |
2c646c80 | 93 | Among equal files, keep the file with the highest link count. |
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94 | |
95 | *-M*, *--minimize*:: | |
2c646c80 | 96 | Among equal files, keep the file with the lowest link count. |
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97 | |
98 | *-O*, *--keep-oldest*:: | |
2c646c80 | 99 | 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. |
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100 | |
101 | *-x*, *--exclude* _regex_:: | |
2c646c80 | 102 | A regular expression which excludes files from being compared and linked. |
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103 | |
104 | *-i*, *--include* _regex_:: | |
2c646c80 | 105 | 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. |
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106 | |
107 | *-s*, *--minimum-size* _size_:: | |
2c646c80 | 108 | 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"). |
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110 | *-S*, *--maximum-size* _size_:: |
111 | 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"). | |
112 | ||
64c8db3c | 113 | *-b*, *--io-size* _size_:: |
344b0cd4 | 114 | The size of the *read*(2) or *sendfile*(2) buffer used when comparing file contents. |
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115 | The _size_ argument may be followed by the multiplicative suffixes KiB, MiB, |
116 | etc. The "iB" is optional, e.g., "K" has the same meaning as "KiB". The | |
117 | default is 8KiB for memcmp method and 1MiB for the other methods. The only | |
118 | memcmp method uses process memory for the buffer, other methods use zero-copy | |
119 | way and I/O operation is done in the kernel. The size may be altered on the fly | |
120 | to fit a number of cached content checksums. | |
121 | ||
122 | *-r*, *--cache-size* _size_:: | |
123 | The size of the cache for content checksums. All non-memcmp methods calculate checksum for each | |
344b0cd4 | 124 | file content block (see *--io-size*), these checksums are cached for the next comparison. The |
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125 | size is important for large files or a large sets of files of the same size. The default is |
126 | 10MiB. | |
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128 | == ARGUMENTS |
129 | ||
130 | *hardlink* takes one or more directories which will be searched for files to be linked. | |
131 | ||
132 | == BUGS | |
133 | ||
bd67ca44 | 134 | 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*. |
6c64d12d | 135 | |
e6743239 | 136 | *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. |
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137 | |
138 | == AUTHOR | |
139 | ||
140 | 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. | |
141 | ||
625e9c61 | 142 | include::man-common/bugreports.adoc[] |
6c64d12d | 143 | |
625e9c61 | 144 | include::man-common/footer.adoc[] |
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145 | |
146 | ifdef::translation[] | |
625e9c61 | 147 | include::man-common/translation.adoc[] |
6c64d12d | 148 | endif::[] |