fastrm(1)



FASTRM(1)                 InterNetNews Documentation                 FASTRM(1)

NAME
       fastrm - Quickly remove a list of files

SYNOPSIS
       fastrm [-de] [-c|-cI] [-s|-sM] [-u|-uN] 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.  fastrm 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 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
       -c[I]
           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).

       -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.

       -s[M]
           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.

       -u[N]
           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 -usr", 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 <patharticles in inn.conf> < expire.list

       To enable all optimizations and see the affect on the order of removal
       caused by -s, use:

           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(2).

       You may want to edit expirerm(8) to change the flags passed to fastrm.

WARNINGS
       fastrm cuts corners and does not worry about security, so it does not
       use chdir(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.

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
       was rewritten in POD by Russ Allbery <eagle@eyrie.org> for
       InterNetNews.

       $Id: fastrm.pod 9767 2014-12-07 21:13:43Z iulius $

SEE ALSO
       expirerm(8).

INN 2.6.1                         2015-09-12                         FASTRM(1)

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