临时目录清理机制

Debian/Ubuntu

/etc/default/rcS 文件中定义了临时目录的清理策略

例如，以下配置文件内容摘自Ubuntu 12.04.4 LTS Server版：

#
# /etc/default/rcS
#
# Default settings for the scripts in /etc/rcS.d/
#
# For information about these variables see the rcS(5) manual page.
#
# This file belongs to the "initscripts" package.

# delete files in /tmp during boot older than x days.
# '0' means always, -1 or 'infinite' disables the feature
TMPTIME=0

# spawn sulogin during boot, continue normal boot if not used in 30 seconds
SULOGIN=no

# do not allow users to log in until the boot has completed
DELAYLOGIN=no

# assume that the BIOS clock is set to UTC time (recommended)
UTC=yes

# be more verbose during the boot process
VERBOSE=no

# automatically repair filesystems with inconsistencies during boot
FSCKFIX=no

其中TMPTIME变量就是控制每次Ubuntu启动时，/tmp目录的清理策略。

RHEL / CentOS / Fedora / Redhat Linux

/etc/cron.daily/tmpwatch 是一个shell脚本，用于每天定时清理一段时间（默认为30天）没有被访问过的普通文件。注意，tmpwatch这个shell脚本在默认最小化安装时是不会被安装的，需要手工yum install tmpwatch。

shell脚本中使用临时文件

使用到外部程序mktemp ，详细用法可以man mktemp，以下实例代码摘自/usb/bin/xvfb-run：

#!/bin/sh
# --- T2-COPYRIGHT-NOTE-BEGIN ---
# This copyright note is auto-generated by ./scripts/Create-CopyPatch.
# 
# T2 SDE: package/.../xorg-server/xvfb-run.sh
# Copyright (C) 2005 The T2 SDE Project
# Copyright (C) XXXX - 2005 Debian
# 
# More information can be found in the files COPYING and README.
# 
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 2 of the License. A copy of the
# GNU General Public License can be found in the file COPYING.
# --- T2-COPYRIGHT-NOTE-END ---

# $Id$
# from: http://necrotic.deadbeast.net/xsf/XFree86/trunk/debian/local/xvfb-run

# This script starts an instance of Xvfb, the "fake" X server, runs a command
# with that server available, and kills the X server when done.  The return
# value of the command becomes the return value of this script.
#
# If anyone is using this to build a Debian package, make sure the package
# Build-Depends on xvfb, xbase-clients, and xfonts-base.

set -e

PROGNAME=xvfb-run
SERVERNUM=99
AUTHFILE=
ERRORFILE=/dev/null
STARTWAIT=3
XVFBARGS="-screen 0 640x480x8"
LISTENTCP="-nolisten tcp"
XAUTHPROTO=.

# Query the terminal to establish a default number of columns to use for
# displaying messages to the user.  This is used only as a fallback in the event
# the COLUMNS variable is not set.  ($COLUMNS can react to SIGWINCH while the
# script is running, and this cannot, only being calculated once.)
DEFCOLUMNS=$(stty size 2>/dev/null | awk '{print $2}') || true
if ! expr "$DEFCOLUMNS" : "[[:digit:]]\+$" >/dev/null 2>&1; then
    DEFCOLUMNS=80
fi

# Display a message, wrapping lines at the terminal width.
message () {
    echo "$PROGNAME: $*" | fmt -t -w ${COLUMNS:-$DEFCOLUMNS}
}

# Display an error message.
error () {
    message "error: $*" >&2
}

# Display a usage message.
usage () {
    if [ -n "$*" ]; then
        message "usage error: $*"
    fi
    cat <<EOF
Usage: $PROGNAME [OPTION ...] COMMAND
Run COMMAND (usually an X client) in a virtual X server environment.
Options:
-a        --auto-servernum          try to get a free server number, starting at
                                    --server-num
-e FILE   --error-file=FILE         file used to store xauth errors and Xvfb
                                    output (default: $ERRORFILE)
-f FILE   --auth-file=FILE          file used to store auth cookie
                                    (default: ./.Xauthority)
-h        --help                    display this usage message and exit
-n NUM    --server-num=NUM          server number to use (default: $SERVERNUM)
-l        --listen-tcp              enable TCP port listening in the X server
-p PROTO  --xauth-protocol=PROTO    X authority protocol name to use
                                    (default: xauth command's default)
-s ARGS   --server-args=ARGS        arguments (other than server number and
                                    "-nolisten tcp") to pass to the Xvfb server
                                    (default: "$XVFBARGS")
-w DELAY  --wait=DELAY              delay in seconds to wait for Xvfb to start
                                    before running COMMAND (default: $STARTWAIT)
EOF
}

# Find a free server number by looking at .X*-lock files in /tmp.
find_free_servernum() {
    # Sadly, the "local" keyword is not POSIX.  Leave the next line commented in
    # the hope Debian Policy eventually changes to allow it in /bin/sh scripts
    # anyway.
    #local i

    i=$SERVERNUM
    while [ -f /tmp/.X$i-lock ]; do
        i=$(($i + 1))
    done
    echo $i
}

# Parse the command line.
ARGS=$(getopt --options +ae:f:hn:lp:s:w: \
       --long auto-servernum,error-file:auth-file:,help,server-num:,listen-tcp,xauth-protocol:,server-args:,wait: \
       --name "$PROGNAME" -- "$@")
GETOPT_STATUS=$?

if [ $GETOPT_STATUS -ne 0 ]; then
    error "internal error; getopt exited with status $GETOPT_STATUS"
    exit 6
fi

eval set -- "$ARGS"

while :; do
    case "$1" in
        -a|--auto-servernum) SERVERNUM=$(find_free_servernum) ;;
        -e|--error-file) ERRORFILE="$2"; shift ;;
        -f|--auth-file) AUTHFILE="$2"; shift ;;
        -h|--help) SHOWHELP="yes" ;;
        -n|--server-num) SERVERNUM="$2"; shift ;;
        -l|--listen-tcp) LISTENTCP="" ;;
        -p|--xauth-protocol) XAUTHPROTO="$2"; shift ;;
        -s|--server-args) XVFBARGS="$2"; shift ;;
        -w|--wait) STARTWAIT="$2"; shift ;;
        --) shift; break ;;
        *) error "internal error; getopt permitted \"$1\" unexpectedly"
           exit 6
           ;;
    esac
    shift
done

if [ "$SHOWHELP" ]; then
    usage
    exit 0
fi

if [ -z "$*" ]; then
    usage "need a command to run" >&2
    exit 2
fi

if ! which xauth >/dev/null; then
    error "xauth command not found"
    exit 3
fi

# If the user did not specify an X authorization file to use, set up a temporary
# directory to house one.
if [ -z "$AUTHFILE" ]; then
    XVFB_RUN_TMPDIR="$(mktemp --directory --tmpdir $PROGNAME.XXXXXX)"
    AUTHFILE=$(mktemp -p "$XVFB_RUN_TMPDIR" Xauthority.XXXXXX)
fi

# Start Xvfb.
MCOOKIE=$(mcookie)

XAUTHORITY=$AUTHFILE xauth source - << EOF >>"$ERRORFILE" 2>&1
add :$SERVERNUM $XAUTHPROTO $MCOOKIE
EOF
XAUTHORITY=$AUTHFILE Xvfb ":$SERVERNUM" $XVFBARGS $LISTENTCP >>"$ERRORFILE" \
  2>&1 &
XVFBPID=$!
sleep "$STARTWAIT"

# Start the command and save its exit status.
set +e
DISPLAY=:$SERVERNUM XAUTHORITY=$AUTHFILE "$@" 2>&1
RETVAL=$?
set -e

# Kill Xvfb now that the command has exited.
kill $XVFBPID

# Clean up.
XAUTHORITY=$AUTHFILE xauth remove ":$SERVERNUM" >"$ERRORFILE" 2>&1
if [ -n "$XVFB_RUN_TMPDIR" ]; then
    if ! rm -r "$XVFB_RUN_TMPDIR"; then
        error "problem while cleaning up temporary directory"
        exit 5
    fi
fi

# Return the executed command's exit status.
exit $RETVAL

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