fastrm - Quickly remove a list of files
] [ -u
reads a list of either file names or storage API tokens, one per
line, from its standard input and removes them. Storage API tokens are removed
via the SMcancel()
does not delete files
safely or with an eye to security, but rather cuts every corner it can to
delete files as fast as it can. It should therefore never be run on publically
writable directories, or in any other environment where a hostile party may
control the directory structure in which it is working.
If a file name is not an absolute path name, it is considered to be relative to
as given on the command line. The base-directory
parameter must be a simple absolute pathname (it must not contain multiple
consecutive slashes or references to the special directories "." or
is designed to be faster than the typical "| xargs rm"
pipeline when given a sorted list of file names as input. For example,
will usually chdir
(2) into a directory before removing
files from it, meaning that if its input is sorted, most names passed to
(2) will be simple names. This can substantially reduce the
operating system overhead from directory lookups.
assumes that its input is valid and that it is safe to call
(2) on every file name it is given. As a safety measure, however,
when running as root will check with stat
(2) that a file
name doesn't specify a directory before removing it. (In some operating
systems, root is allowed to unlink directories, even directories which aren't
empty, which can cause file system corruption.)
The input to fastrm
should always be sorted -- or even better be
in the order file names are output by find
(1) -- if speed is an
issue and the input isn't solely storage API tokens. (It deals fine with
unsorted input, but is unlikely to be any faster in that case than a simple
"| xargs rm" command.) Sorting may even slightly speed up the
removal of storage API tokens due to caching effects, since sorting will tend
to keep all of the tokens from a particular storage method together.
Various additional optimizations for removing files can be turned on and/or
tuned with options (see below). Which options will be most effective depends
heavily on the underlying structure of the file system, the way in which
directories are stored and searched, and similar, often underdocumented,
operating system implementation details. The more sophisticated the underlying
operating system and file system, the more likely that it will already perform
the equivalent of these optimizations internally.
- Controls when fastrm calls chdir(2). If the
number of files to be unlinked from a given directory is at least
I, then fastrm will change to that directory before
unlinking those files. Otherwise, it will use either the absolute path
names or a path name relative to the current directory (whichever is
likely more efficient). The I parameter is optional; if just
-c is given, -c1 is assumed, which will cause fastrm
to always chdir before calling unlink(2). The default is
-c3. Use -c0 to prevent fastrm from ever using
- Don't remove any files. Instead, print a list of the files
that would be removed to standard output. Each line contains either the
current directory of fastrm at the time it would do the unlink and
the relative path name it would pass to unlink(2) as two fields
separated by whitespace and a "/", the absolute path name (as a
single field) that would be passed to unlink(2), or the string
"Token" and the storage API token that would be removed.
- Treat an empty input file as an error. This is most useful
when fastrm is last in a pipeline after a preceding sort(1)
command, ensuring that fastrm will fail if the sort fails.
- When -s is given and the number of files to remove
in a directory is greater than M, rather than remove files in the
order given, fastrm will open the directory and read it, unlinking
files in the order that they appear in the directory. On systems with a
per-process directory cache or that use a linear search to find files in a
directory, this should make directory lookups faster. The M
parameter is optional; if just -s is given, -s5 is assumed.
When this option is in effect, fastrm won't attempt to remove files
that it doesn't see in the directory, possibly significantly speeding it
up if most of the files to be removed have already been deleted. However,
using this option requires fastrm to do more internal work and it
also assumes that the order of directory listings is stable in the
presence of calls to unlink(2) between calls to readdir(3).
This may be a dangerous assumption with some sophisticated file systems
(and in general this option is only useful with file systems that use
unindexed linear searches to find files in directories or when most of the
files to be removed have already been deleted).
This optimization is off by default.
- Specifying this option promises that there are no symbolic
links in the directory tree from which files are being removed. This
allows fastrm to make an additional optimization to its calls to
chdir(2), constructing a relative path using "../.." and
the like to pass to chdir(2) rather than always using absolute
paths. Since this reduces the number of directory lookups needed with
deeply nested directory structures (such as that typically created by
traditional news spool storage), it can be a significant optimization, but
it breaks horribly in the presence of symbolic links to directories.
When -u is given, fastrm will use at most N levels of
".." segments to construct paths. N is optional; if just
-u is given, -u1 is assumed.
This optimization is off by default.
also accepts -a
options, which do nothing at
all except allow you to say "fastrm -usa", "fastrm -usr",
or "fastrm -user". These happen to often be convenient sets of
options to use.
exits with a status of zero if there were no problems, and an exit
status of 1 if something went wrong. Attempting to remove a file that does not
exist is not considered a problem.
is typically invoked by INN via expirerm
(8) using a command
fastrm -e <patharticles in inn.conf> < expire.list
To enable all optimizations and see the affect on the order of removal caused by
fastrm -d -s -e -u <patharticles> < expire.list
If your file system has indexed directory lookups, but you have a deeply nested
directory structure, you may want to use a set of flags like:
fastrm -e -u3 <patharticles> < expire.list
to strongly prefer relative paths but not to use readdir
(2) to order the
calls to unlink
You may want to edit expirerm
(8) to change the flags passed to
cuts corners and does not worry about security, so it does not use
(2) safely and could be tricked into removing files other than
those that were intended if run on a specially constructed file tree or a file
tree that is being modified while it is running. It should therefore never be
used with world-writable directories or any other directory that might be
controlled or modified by an attacker.
defers opening the storage subsystem or attempting to parse any
INN configuration files until it encounters a token in the list of files to
remove. It's therefore possible to use fastrm
outside of INN as a
general fast file removal program.
was originally written by <firstname.lastname@example.org>. This manual
page was rewritten in POD by Russ Allbery <email@example.com> for
$Id: fastrm.pod 9767 2014-12-07 21:13:43Z iulius $