1FASTRM(1) InterNetNews Documentation FASTRM(1)
2
6 fastrm - Quickly remove a list of files
7
9 fastrm [-de] [-u⎪-uN] [-s⎪-sM] [-c⎪-cI] base-directory
10
12 fastrm reads a list of either file names or storage API tokens, one per
13 line, from its standard input and removes them. Storage API tokens are
14 removed via the SMcancel() interface. fastrm does not delete files
15 safely or with an eye to security, but rather cuts every corner it can
16 to delete files as fast as it can. It should therefore never be run on
17 publically writable directories, or in any other environment where a
18 hostile party may control the directory structure in which it is work‐
19 ing.
20 If a file name is not an absolute path name, it is considered to be
22 relative to base-directory as given on the command line. The base-
23 directory parameter must be a simple absolute pathname (it must not
24 contain multiple consecutive slashes or references to the special
25 directories "." or "..").
26 fastrm is designed to be faster than the typical "⎪ xargs rm" pipeline
28 when given a sorted list of file names as input. For example, fastrm
29 will usually chdir(2) into a directory before removing files from it,
30 meaning that if its input is sorted, most names passed to unlink(2)
31 will be simple names. This can substantially reduce the operating sys‐
32 tem overhead from directory lookups.
33 fastrm assumes that its input is valid and that it is safe to call
35 unlink(2) on every file name it is given. As a safety measure, how‐
36 ever, fastrm when running as root will check with stat(2) that a file
37 name doesn't specify a directory before removing it. (In some operat‐
38 ing systems, root is allowed to unlink directories, even directories
39 which aren't empty, which can cause file system corruption.)
40 The input to fastrm should always be sorted -- or even better be in the
42 order file names are output by find(1) -- if speed is an issue and the
43 input isn't solely storage API tokens. (It deals fine with unsorted
44 input, but is unlikely to be any faster in that case than a simple
45 "xargs rm" command.) Sorting may even slightly speed up the removal of
46 storage API tokens due to caching effects, since sorting will tend to
47 keep all of the tokens from a particular storage method together.
48 Various additional optimizations for removing files can be turned on
50 and/or tuned with options (see below). Which options will be most
51 effective depends heavily on the underlying structure of the file sys‐
52 tem, the way in which directories are stored and searched, and similar,
53 often underdocumented, operating system implementation details. The
54 more sophisticated the underlying operating system and file system, the
55 more likely that it will already perform the equivalent of these opti‐
56 mizations internally.
57
59 -d Don't remove any files. Instead, print a list of the files that
60 would be removed to standard output. Each line contains either the
61 current directory of fastrm at the time it would do the unlink and
62 the relative path name it would pass to unlink(2) as two fields
63 separated by whitespace and a "/", the absolute path name (as a
64 single field) that would be passed to unlink(2), or the string
65 "Token" and the storage API token that would be removed.
66 -e Treat an empty input file as an error. This is most useful when
68 fastrm is last in a pipeline after a preceding sort(1) command,
69 ensuring that fastrm will fail if the sort fails.
70 -cI Controls when fastrm calls chdir(2). If the number of files to be
72 unlinked from a given directory is at least I, then fastrm will
73 change to that directory before unlinking those files. Otherwise,
74 it will use either the absolute path names or a path name relative
75 to the current directory (whichever is likely more efficient). The
76 I parameter is optional; if just -c is given, -c1 is assumed, which
77 will cause fastrm to always chdir before calling unlink(2). The
78 default is -c3. Use -c0 to prevent fastrm from ever using
79 chdir(2).
80 -sM When -s is given and the number of files to remove in a directory
82 is greater than M, rather than remove files in the order given,
83 fastrm will open the directory and read it, unlinking files in the
84 order that they appear in the directory. On systems with a per-
85 process directory cache or that use a linear search to find files
86 in a directory, this should make directory lookups faster. The M
87 parameter is optional; if just -s is given, -s5 is assumed.
88 When this option is in effect, fastrm won't attempt to remove files
90 that it doesn't see in the directory, possibly significantly speed‐
91 ing it up if most of the files to be removed have already been
92 deleted. However, using this option requires fastrm to do more
93 internal work and it also assumes that the order of directory list‐
94 ings is stable in the presence of calls to unlink(2) between calls
95 to readdir(3). This may be a dangerous assumption with some
96 sophisticated file systems (and in general this option is only use‐
97 ful with file systems that use unindexed linear searches to find
98 files in directories or when most of the files to be removed have
99 already been deleted).
100 This optimization is off by default.
102 -uN Specifying this option promises that there are no symbolic links in
104 the directory tree from which files are being removed. This allows
105 fastrm to make an additional optimization to its calls to chdir(2),
106 constructing a relative path using "../.." and the like to pass to
107 chdir(2) rather than always using absolute paths. Since this
108 reduces the number of directory lookups needed with deeply nested
109 directory structures (such as that typically created by traditional
110 news spool storage), it can be a significant optimization, but it
111 breaks horribly in the presence of symbolic links to directories.
112 When -u is given, fastrm will use at most N levels of ".." seg‐
114 ments to construct paths. N is optional; if just -u is given, -u1
115 is assumed.
116 This optimization is off by default.
118 fastrm also accepts -a and -r options, which do nothing at all except
120 allow you to say "fastrm -usa", "fastrm -ussr", or "fastrm -user".
121 These happen to often be convenient sets of options to use.
122
124 fastrm exits with a status of zero if there were no problems, and an
125 exit status of 1 if something went wrong. Attempting to remove a file
126 that does not exist is not considered a problem.
127
129 fastrm is typically invoked by INN via expirerm(8) using a command
130 like:
131 fastrm -e /usr/local/news/spool/articles < expire.list
133 To enable all optimizations and see the affect on the order of removal
135 caused by -s, use:
136 fastrm -d -s -e -u ~news/spool/articles < expire.list
138 If your file system has indexed directory lookups, but you have a
140 deeply nested directory structure, you may want to use a set of flags
141 like:
142 fastrm -e -u3 ~news/spool/articles < expire.list
144 to strongly prefer relative paths but not to use readdir(2) to order
146 the calls to unlink(2).
147 You may want to edit expirerm(8) to change the flags passed to fastrm.
149
151 fastrm cuts corners and does not worry about security, so it does not
152 use chdir(2) safely and could be tricked into removing files other than
153 those that were intended if run on a specially constructed file tree or
154 a file tree that is being modified while it is running. It should
155 therefore never be used with world-writable directories or any other
156 directory that might be controlled or modified by an attacker.
157
159 fastrm defers opening the storage subsystem or attempting to parse any
160 INN configuration files until it encounters a token in the list of
161 files to remove. It's therefore possible to use fastrm outside of INN
162 as a general fast file removal program.
163
165 fastrm was originally written by kre@munnari.oz.au. This manual page
166 rewritten in POD by Russ Allbery <rra@stanford.edu> for InterNetNews.
167 $Id: fastrm.1 7429 2005-12-11 20:42:43Z eagle $
169
171 expirerm(8)
172INN 2.4.3 2005-10-08 FASTRM(1)