LDP/LDP/guide/docbook/abs-guide/ex73.sh

#!/bin/bash
# Creating a swap file.

#  A swap file provides a temporary storage cache
#+ which helps speed up certain filesystem operations.

ROOT_UID=0         # Root has $UID 0.
E_WRONG_USER=85    # Not root?

FILE=/swap
BLOCKSIZE=1024
MINBLOCKS=40
SUCCESS=0


# This script must be run as root.
if [ "$UID" -ne "$ROOT_UID" ]
then
  echo; echo "You must be root to run this script."; echo
  exit $E_WRONG_USER
fi  
  

blocks=${1:-$MINBLOCKS}          #  Set to default of 40 blocks,
                                 #+ if nothing specified on command-line.
# This is the equivalent of the command block below.
# --------------------------------------------------
# if [ -n "$1" ]
# then
#   blocks=$1
# else
#   blocks=$MINBLOCKS
# fi
# --------------------------------------------------


if [ "$blocks" -lt $MINBLOCKS ]
then
  blocks=$MINBLOCKS              # Must be at least 40 blocks long.
fi  


######################################################################
echo "Creating swap file of size $blocks blocks (KB)."
dd if=/dev/zero of=$FILE bs=$BLOCKSIZE count=$blocks  # Zero out file.
mkswap $FILE $blocks             # Designate it a swap file.
swapon $FILE                     # Activate swap file.
retcode=$?                       # Everything worked?
#  Note that if one or more of these commands fails,
#+ then it could cause nasty problems.
######################################################################

#  Exercise:
#  Rewrite the above block of code so that if it does not execute
#+ successfully, then:
#    1) an error message is echoed to stderr,
#    2) all temporary files are cleaned up, and
#    3) the script exits in an orderly fashion with an
#+      appropriate error code.

echo "Swap file created and activated."

exit $retcode