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FASTRM(1)
NAME
fastrm - Quickly remove a list of files
SYNOPSIS
fastrm [-de] [-u|-uN] [-s|-sM] [-c|-cI] base-directory
DESCRIPTION
fastrm 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() interface.
If a file name is not an absolute path name, it is considered to be
relative to base-directory 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 "..").
fastrm is designed to be faster than the typical "| xargs rm" pipeline when
given a sorted list of file names as input. For example, fastrm will
usually chdir(2) into a directory before removing files from it, meaning
that if its input is sorted, most names passed to unlink(2) will be simple
names. This can substantially reduce the operating system overhead from
directory lookups.
fastrm assumes that its input is valid and that it is safe to call
unlink(2) on every file name it is given. As a safety measure, however,
fastrm 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.
OPTIONS
-d 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.
-e 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.
-cI 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 chdir(2).
-sM 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.
-uN 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.
fastrm also accepts -a and -r options, which do nothing at all except allow
you to say "fastrm -usa", "fastrm -ussr", or "fastrm -user". These happen
to often be convenient sets of options to use.
EXIT STATUS
fastrm 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.
EXAMPLES
fastrm is typically invoked by INN via expirerm(8) using a command like:
fastrm -e /usr/local/news/spool/articles < expire.list
To enable all optimizations and see the affect on the order of removal
caused by -s, use:
fastrm -d -s -e -u ~news/spool/articles < 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 ~news/spool/articles < expire.list
to strongly prefer relative paths but not to use readdir(2) to order the
calls to unlink(2).
You may want to edit expirerm(8) to change the flags passed to fastrm.
NOTES
fastrm 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.
HISTORY
fastrm was originally written by kre@munnari.oz.au. This manual page
rewritten in POD by Russ Allbery <rra@stanford.edu> for InterNetNews.
$Id: fastrm.1,v 1.1.2.1 2001/02/03 07:38:44 rra Exp $
SEE ALSO
expirerm(8)
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