Compressing Man and Info Pages

Man and info reader programs can transparently process files compressed with gzip or bzip2, a feature you can use to free some disk space while keeping your documentation available. However, things are not that simple; man directories tend to contain links—hard and symbolic—which defeat simple ideas like recursively calling gzip on them. A better way to go is to use the script below. If you would prefer to download the file instead of creating it by typing or cut-and-pasting, you can find it at http://anduin.linuxfromscratch.org/files/BLFS/6.3/compressdoc (the file should be installed in the /usr/sbin directory).

cat > /usr/sbin/compressdoc << "EOF"
#!/bin/bash
# VERSION: 20080421.1623
#
# Compress (with bzip2 or gzip) all man pages in a hierarchy and
# update symlinks - By Marc Heerdink <marc @ koelkast.net>
#
# Modified to be able to gzip or bzip2 files as an option and to deal
# with all symlinks properly by Mark Hymers <markh @ linuxfromscratch.org>
#
# Modified 20030930 by Yann E. Morin <yann.morin.1998 @ anciens.enib.fr>
# to accept compression/decompression, to correctly handle hard-links,
# to allow for changing hard-links into soft- ones, to specify the
# compression level, to parse the man.conf for all occurrences of MANPATH,
# to allow for a backup, to allow to keep the newest version of a page.
#
# Modified 20040330 by Tushar Teredesai to replace $0 by the name of the
# script.
#   (Note: It is assumed that the script is in the user's PATH)
#
# Modified 20050112 by Randy McMurchy to shorten line lengths and
# correct grammar errors.
#
# Modified 20060128 by Alexander E. Patrakov for compatibility with Man-DB.
#
# Modified 20060311 by Archaic to use Man-DB manpath utility which is a
# replacement for man --path from Man.
#
# Modified 20080421 by Dan Nicholson to properly execute the correct
# compressdoc when working recursively. This means the same compressdoc
# will be used whether a full path was given or it was resolved from PATH.
#
# Modified 20080421 by Dan Nicholson to be more robust with directories
# that don't exist or don't have sufficient permissions.
#
# Modified 20080421 by Lars Bamberger to (sort of) automatically choose
# a compression method based on the size of the manpage. A couple bug
# fixes were added by Dan Nicholson.
#
# Modified 20080421 by Dan Nicholson to suppress warnings from manpath
# since these are emitted when $MANPATH is set. Removed the TODO for
# using the $MANPATH variable since manpath(1) handles this already.
#
# TODO:
#     - choose a default compress method to be based on the available
#       tool : gzip or bzip2;
#     - offer an option to restore a previous backup;
#     - add other compression engines (compress, zip, etc?). Needed?

# Funny enough, this function prints some help.
function help ()
{
  if [ -n "$1" ]; then
    echo "Unknown option : $1"
  fi
  ( echo "Usage: $MY_NAME <comp_method> [options] [dirs]" && \
  cat << EOT
Where comp_method is one of :
  --gzip, --gz, -g
  --bzip2, --bz2, -b
                Compress using gzip or bzip2.
  --automatic
                Compress using either gzip or bzip2, depending on the
                size of the file to be compressed. Files larger than 5
                kB are bzipped, files larger than 1 kB are gzipped and
                files smaller than 1 kB are not compressed.

  --decompress, -d
                Decompress the man pages.

  --backup      Specify a .tar backup shall be done for all directories.
                In case a backup already exists, it is saved as .tar.old
                prior to making the new backup. If a .tar.old backup
                exists, it is removed prior to saving the backup.
                In backup mode, no other action is performed.

And where options are :
  -1 to -9, --fast, --best
                The compression level, as accepted by gzip and bzip2.
                When not specified, uses the default compression level
                for the given method (-6 for gzip, and -9 for bzip2).
                Not used when in backup or decompress modes.

  --force, -F   Force (re-)compression, even if the previous one was
                the same method. Useful when changing the compression
                ratio. By default, a page will not be re-compressed if
                it ends with the same suffix as the method adds
                (.bz2 for bzip2, .gz for gzip).

  --soft, -S    Change hard-links into soft-links. Use with _caution_
                as the first encountered file will be used as a
                reference. Not used when in backup mode.

  --hard, -H    Change soft-links into hard-links. Not used when in
                backup mode.

  --conf=dir, --conf dir
                Specify the location of man_db.conf. Defaults to /etc.

  --verbose, -v Verbose mode, print the name of the directory being
                processed. Double the flag to turn it even more verbose,
                and to print the name of the file being processed.

  --fake, -f    Fakes it. Print the actual parameters compressdoc will use.

  dirs          A list of space-separated _absolute_ pathnames to the
                man directories. When empty, and only then, use manpath
                to parse ${MAN_CONF}/man_db.conf for all valid occurrences
                of MANDATORY_MANPATH.

Note about compression:
  There has been a discussion on blfs-support about compression ratios of
  both gzip and bzip2 on man pages, taking into account the hosting fs,
  the architecture, etc... On the overall, the conclusion was that gzip
  was much more efficient on 'small' files, and bzip2 on 'big' files,
  small and big being very dependent on the content of the files.

  See the original post from Mickael A. Peters, titled
  "Bootable Utility CD", dated 20030409.1816(+0200), and subsequent posts:
  http://linuxfromscratch.org/pipermail/blfs-support/2003-April/038817.html

  On my system (x86, ext3), man pages were 35564KB before compression.
  gzip -9 compressed them down to 20372KB (57.28%), bzip2 -9 got down to
  19812KB (55.71%). That is a 1.57% gain in space. YMMV.

  What was not taken into consideration was the decompression speed. But
  does it make sense to? You gain fast access with uncompressed man
  pages, or you gain space at the expense of a slight overhead in time.
  Well, my P4-2.5GHz does not even let me notice this... :-)

EOT
) | less
}

# This function checks that the man page is unique amongst bzip2'd,
# gzip'd and uncompressed versions.
#  $1 the directory in which the file resides
#  $2 the file name for the man page
# Returns 0 (true) if the file is the latest and must be taken care of,
# and 1 (false) if the file is not the latest (and has therefore been
# deleted).
function check_unique ()
{
  # NB. When there are hard-links to this file, these are
  # _not_ deleted. In fact, if there are hard-links, they
  # all have the same date/time, thus making them ready
  # for deletion later on.

  # Build the list of all man pages with the same name
  DIR=$1
  BASENAME=`basename "${2}" .bz2`
  BASENAME=`basename "${BASENAME}" .gz`
  GZ_FILE="$BASENAME".gz
  BZ_FILE="$BASENAME".bz2

  # Look for, and keep, the most recent one
  LATEST=`(cd "$DIR"; ls -1rt "${BASENAME}" "${GZ_FILE}" "${BZ_FILE}" \
         2>/dev/null | tail -n 1)`
  for i in "${BASENAME}" "${GZ_FILE}" "${BZ_FILE}"; do
    [ "$LATEST" != "$i" ] && rm -f "$DIR"/"$i"
  done

  # In case the specified file was the latest, return 0
  [ "$LATEST" = "$2" ] && return 0
  # If the file was not the latest, return 1
  return 1
}

# Name of the script
MY_NAME=`basename $0`

# OK, parse the command-line for arguments, and initialize to some
# sensible state, that is: don't change links state, parse
# /etc/man_db.conf, be most silent, search man_db.conf in /etc, and don't
# force (re-)compression.
COMP_METHOD=
COMP_SUF=
COMP_LVL=
FORCE_OPT=
LN_OPT=
MAN_DIR=
VERBOSE_LVL=0
BACKUP=no
FAKE=no
MAN_CONF=/etc
while [ -n "$1" ]; do
  case $1 in
    --gzip|--gz|-g)
      COMP_SUF=.gz
      COMP_METHOD=$1
      shift
      ;;
    --bzip2|--bz2|-b)
      COMP_SUF=.bz2
      COMP_METHOD=$1
      shift
      ;;
    --automatic)
      COMP_SUF=TBD
      COMP_METHOD=$1
      shift
      ;;
    --decompress|-d)
      COMP_SUF=
      COMP_LVL=
      COMP_METHOD=$1
      shift
      ;;
    -[1-9]|--fast|--best)
      COMP_LVL=$1
      shift
      ;;
    --force|-F)
      FORCE_OPT=-F
      shift
      ;;
    --soft|-S)
      LN_OPT=-S
      shift
      ;;
    --hard|-H)
      LN_OPT=-H
      shift
      ;;
    --conf=*)
      MAN_CONF=`echo $1 | cut -d '=' -f2-`
      shift
      ;;
    --conf)
      MAN_CONF="$2"
      shift 2
      ;;
    --verbose|-v)
      let VERBOSE_LVL++
      shift
      ;;
    --backup)
      BACKUP=yes
      shift
      ;;
    --fake|-f)
      FAKE=yes
      shift
      ;;
    --help|-h)
      help
      exit 0
      ;;
    /*)
      MAN_DIR="${MAN_DIR} ${1}"
      shift
      ;;
    -*)
      help $1
      exit 1
      ;;
    *)
      echo "\"$1\" is not an absolute path name"
      exit 1
      ;;
  esac
done

# Redirections
case $VERBOSE_LVL in
  0)
     # O, be silent
     DEST_FD0=/dev/null
     DEST_FD1=/dev/null
     VERBOSE_OPT=
     ;;
  1)
     # 1, be a bit verbose
     DEST_FD0=/dev/stdout
     DEST_FD1=/dev/null
     VERBOSE_OPT=-v
     ;;
  *)
     # 2 and above, be most verbose
     DEST_FD0=/dev/stdout
     DEST_FD1=/dev/stdout
     VERBOSE_OPT="-v -v"
     ;;
esac

# Note: on my machine, 'man --path' gives /usr/share/man twice, once
# with a trailing '/', once without.
if [ -z "$MAN_DIR" ]; then
  MAN_DIR=`manpath -q -C "$MAN_CONF"/man_db.conf \
            | sed 's/:/\\n/g' \
            | while read foo; do dirname "$foo"/.; done \
            | sort -u \
            | while read bar; do echo -n "$bar "; done`
fi

# If no MANDATORY_MANPATH in ${MAN_CONF}/man_db.conf, abort as well
if [ -z "$MAN_DIR" ]; then
  echo "No directory specified, and no directory found with \`manpath'"
  exit 1
fi

# Check that the specified directories actually exist and are readable
for DIR in $MAN_DIR; do
  if [ ! -d "$DIR" -o ! -r "$DIR" ]; then
    echo "Directory '$DIR' does not exist or is not readable"
    exit 1
  fi
done

# Fake?
if [ "$FAKE" != "no" ]; then
  echo "Actual parameters used:"
  echo -n "Compression.......: "
  case $COMP_METHOD in
    --bzip2|--bz2|-b) echo -n "bzip2";;
    --gzip|--gz|-g) echo -n "gzip";;
    --automatic) echo -n "compressing";;
    --decompress|-d) echo -n "decompressing";;
    *) echo -n "unknown";;
  esac
  echo " ($COMP_METHOD)"
  echo "Compression level.: $COMP_LVL"
  echo "Compression suffix: $COMP_SUF"
  echo -n "Force compression.: "
  [ "foo$FORCE_OPT" = "foo-F" ] && echo "yes" || echo "no"
  echo "man_db.conf is....: ${MAN_CONF}/man_db.conf"
  echo -n "Hard-links........: "
  [ "foo$LN_OPT" = "foo-S" ] &&
  echo "convert to soft-links" || echo "leave as is"
  echo -n "Soft-links........: "
  [ "foo$LN_OPT" = "foo-H" ] &&
  echo "convert to hard-links" || echo "leave as is"
  echo "Backup............: $BACKUP"
  echo "Faking (yes!).....: $FAKE"
  echo "Directories.......: $MAN_DIR"
  echo "Verbosity level...: $VERBOSE_LVL"
  exit 0
fi

# If no method was specified, print help
if [ -z "${COMP_METHOD}" -a "${BACKUP}" = "no" ]; then
  help
  exit 1
fi

# In backup mode, do the backup solely
if [ "$BACKUP" = "yes" ]; then
  for DIR in $MAN_DIR; do
    cd "${DIR}/.."
    if [ ! -w "`pwd`" ]; then
      echo "Directory '`pwd`' is not writable"
      exit 1
    fi
    DIR_NAME=`basename "${DIR}"`
    echo "Backing up $DIR..." > $DEST_FD0
    [ -f "${DIR_NAME}.tar.old" ] && rm -f "${DIR_NAME}.tar.old"
    [ -f "${DIR_NAME}.tar" ] &&
    mv "${DIR_NAME}.tar" "${DIR_NAME}.tar.old"
    tar -cvf "${DIR_NAME}.tar" "${DIR_NAME}" > $DEST_FD1
  done
  exit 0
fi

# I know MAN_DIR has only absolute path names
# I need to take into account the localized man, so I'm going recursive
for DIR in $MAN_DIR; do
  MEM_DIR=`pwd`
  if [ ! -w "$DIR" ]; then
    echo "Directory '$DIR' is not writable"
    exit 1
  fi
  cd "$DIR"
  for FILE in *; do
    # Fixes the case were the directory is empty
    if [ "foo$FILE" = "foo*" ]; then continue; fi

    # Fixes the case when hard-links see their compression scheme change
    # (from not compressed to compressed, or from bz2 to gz, or from gz
    # to bz2)
    # Also fixes the case when multiple version of the page are present,
    # which are either compressed or not.
    if [ ! -L "$FILE" -a ! -e "$FILE" ]; then continue; fi

    # Do not compress whatis files
    if [ "$FILE" = "whatis" ]; then continue; fi

    if [ -d "$FILE" ]; then
      # We are going recursive to that directory
      echo "-> Entering ${DIR}/${FILE}..." > $DEST_FD0
      # I need not pass --conf, as I specify the directory to work on
      # But I need exit in case of error. We must change back to the
      # original directory so $0 is resolved correctly.
      (cd "$MEM_DIR" && eval "$0" ${COMP_METHOD} ${COMP_LVL} ${LN_OPT} \
        ${VERBOSE_OPT} ${FORCE_OPT} "${DIR}/${FILE}") || exit $?
      echo "<- Leaving ${DIR}/${FILE}." > $DEST_FD1

    else # !dir
      if ! check_unique "$DIR" "$FILE"; then continue; fi

      # With automatic compression, get the uncompressed file size of
      # the file (dereferencing symlinks), and choose an appropriate
      # compression method.
      if [ "$COMP_METHOD" = "--automatic" ]; then
        declare -i SIZE
        case "$FILE" in
          *.bz2)
            SIZE=$(bzcat "$FILE" | wc -c) ;;
          *.gz)
            SIZE=$(zcat "$FILE" | wc -c) ;;
          *)
            SIZE=$(wc -c < "$FILE") ;;
        esac
        if (( $SIZE >= (5 * 2**10) )); then
          COMP_SUF=.bz2
        elif (( $SIZE >= (1 * 2**10) )); then
          COMP_SUF=.gz
        else
          COMP_SUF=
        fi
      fi

      # Check if the file is already compressed with the specified method
      BASE_FILE=`basename "$FILE" .gz`
      BASE_FILE=`basename "$BASE_FILE" .bz2`
      if [ "${FILE}" = "${BASE_FILE}${COMP_SUF}" \
         -a "foo${FORCE_OPT}" = "foo" ]; then continue; fi

      # If we have a symlink
      if [ -h "$FILE" ]; then
        case "$FILE" in
          *.bz2)
            EXT=bz2 ;;
          *.gz)
            EXT=gz ;;
          *)
            EXT=none ;;
        esac

        if [ ! "$EXT" = "none" ]; then
          LINK=`ls -l "$FILE" | cut -d ">" -f2 \
               | tr -d " " | sed s/\.$EXT$//`
          NEWNAME=`echo "$FILE" | sed s/\.$EXT$//`
          mv "$FILE" "$NEWNAME"
          FILE="$NEWNAME"
        else
          LINK=`ls -l "$FILE" | cut -d ">" -f2 | tr -d " "`
        fi

        if [ "$LN_OPT" = "-H" ]; then
          # Change this soft-link into a hard- one
          rm -f "$FILE" && ln "${LINK}$COMP_SUF" "${FILE}$COMP_SUF"
          chmod --reference "${LINK}$COMP_SUF" "${FILE}$COMP_SUF"
        else
          # Keep this soft-link a soft- one.
          rm -f "$FILE" && ln -s "${LINK}$COMP_SUF" "${FILE}$COMP_SUF"
        fi
        echo "Relinked $FILE" > $DEST_FD1

      # else if we have a plain file
      elif [ -f "$FILE" ]; then
        # Take care of hard-links: build the list of files hard-linked
        # to the one we are {de,}compressing.
        # NB. This is not optimum has the file will eventually be
        # compressed as many times it has hard-links. But for now,
        # that's the safe way.
        inode=`ls -li "$FILE" | awk '{print $1}'`
        HLINKS=`find . \! -name "$FILE" -inum $inode`

        if [ -n "$HLINKS" ]; then
          # We have hard-links! Remove them now.
          for i in $HLINKS; do rm -f "$i"; done
        fi

        # Now take care of the file that has no hard-link
        # We do decompress first to re-compress with the selected
        # compression ratio later on...
        case "$FILE" in
          *.bz2)
            bunzip2 $FILE
            FILE=`basename "$FILE" .bz2`
          ;;
          *.gz)
            gunzip $FILE
            FILE=`basename "$FILE" .gz`
          ;;
        esac

        # Compress the file with the given compression ratio, if needed
        case $COMP_SUF in
          *bz2)
            bzip2 ${COMP_LVL} "$FILE" && chmod 644 "${FILE}${COMP_SUF}"
            echo "Compressed $FILE" > $DEST_FD1
            ;;
          *gz)
            gzip ${COMP_LVL} "$FILE" && chmod 644 "${FILE}${COMP_SUF}"
            echo "Compressed $FILE" > $DEST_FD1
            ;;
          *)
            echo "Uncompressed $FILE" > $DEST_FD1
            ;;
        esac

        # If the file had hard-links, recreate those (either hard or soft)
        if [ -n "$HLINKS" ]; then
          for i in $HLINKS; do
            NEWFILE=`echo "$i" | sed s/\.gz$// | sed s/\.bz2$//`
            if [ "$LN_OPT" = "-S" ]; then
              # Make this hard-link a soft- one
              ln -s "${FILE}$COMP_SUF" "${NEWFILE}$COMP_SUF"
            else
              # Keep the hard-link a hard- one
              ln "${FILE}$COMP_SUF" "${NEWFILE}$COMP_SUF"
            fi
            # Really work only for hard-links. Harmless for soft-links
            chmod 644 "${NEWFILE}$COMP_SUF"
          done
        fi

      else
        # There is a problem when we get neither a symlink nor a plain
        # file. Obviously, we shall never ever come here... :-(
        echo -n "Whaooo... \"${DIR}/${FILE}\" is neither a symlink "
        echo "nor a plain file. Please check:"
        ls -l "${DIR}/${FILE}"
        exit 1
      fi
    fi
  done # for FILE
done # for DIR

EOF

As root, make compressdoc executable for all users:

chmod -v 755 /usr/sbin/compressdoc

Now, as root, you can issue the command compressdoc --bz2 to compress all your system man pages. You can also run compressdoc --help to get comprehensive help about what the script is able to do.

Don't forget that a few programs, like the X Window System and XEmacs also install their documentation in non-standard places (such as /usr/X11R6/man, etc.). Be sure to add these locations to the file /etc/man_db.conf, as MANDATORY_MANPATH </path> lines.

Example:

    ...
    MANDATORY_MANPATH                       /usr/share/man
    MANDATORY_MANPATH                       /usr/X11R6/man
    MANDATORY_MANPATH                       /usr/local/man
    MANDATORY_MANPATH                       /opt/qt/doc/man
    ...

Generally, package installation systems do not compress man/info pages, which means you will need to run the script again if you want to keep the size of your documentation as small as possible. Also, note that running the script after upgrading a package is safe; when you have several versions of a page (for example, one compressed and one uncompressed), the most recent one is kept and the others are deleted.

Last updated on 2008-04-21 18:27:43 -0500