方法1: 各应用上电后，getpid（），将自身进程号注册到系统数据库中。编写应用进程，通过周期执行ps -p pidnum 检查指定pid是否存在，不存在则执行相关操作。 方法2： 配置monit服务。 monit服务是开源linux系统监控服务，对应系统配置文件路径为http://mmonit.com/monit/documentation/ 安装：sudo apt-get install monit 配置：sudo vi /etc/monit/monitrc monitrc为monit配置文件，其内容如下：
  ###############################################################################
## Monit control file
###############################################################################
##
## Comments begin with a '#' and extend through the end of the line. Keywords
## are case insensitive. All path's MUST BE FULLY QUALIFIED, starting with '/'.
##
## Below you will find examples of some frequently used statements. For
## information about the control file and a complete list of statements and
## options, please have a look in the Monit manual.
##
##
###############################################################################
## Global section
###############################################################################
##
## Start Monit in the background (run as a daemon):
#
  set daemon 30            # check services at 30 seconds intervals
   with start delay 60
#  with start delay 240    # optional: delay the first check by 4-minutes (by
#                           # default Monit check immediately after Monit start)
#
#
## Set syslog logging with the 'daemon' facility. If the FACILITY option is
## omitted, Monit will use 'user' facility by default. If you want to log to
## a standalone log file instead, specify the full path to the log file
#
# set logfile syslog facility log_daemon                      
  set logfile /var/log/monit.log
#
#
## Set the location of the Monit id file which stores the unique id for the
## Monit instance. The id is generated and stored on first Monit start. By
## default the file is placed in $HOME/.monit.id.
#
# set idfile /var/.monit.id
  set idfile /var/lib/monit/id
#
## Set the location of the Monit state file which saves monitoring states
## on each cycle. By default the file is placed in $HOME/.monit.state. If
## the state file is stored on a persistent filesystem, Monit will recover
## the monitoring state across reboots. If it is on temporary filesystem, the
## state will be lost on reboot which may be convenient in some situations.
#
  set statefile /var/lib/monit/state
#
## Set the list of mail servers for alert delivery. Multiple servers may be
## specified using a comma separator. If the first mail server fails, Monit
# will use the second mail server in the list and so on. By default Monit uses
# port 25 - it is possible to override this with the PORT option.
#
# set mailserver mail.bar.baz,               # primary mailserver
#                backup.bar.baz port 10025,  # backup mailserver on port 10025
#                localhost                   # fallback relay
#
#
## By default Monit will drop alert events if no mail servers are available.
## If you want to keep the alerts for later delivery retry, you can use the
## EVENTQUEUE statement. The base directory where undelivered alerts will be
## stored is specified by the BASEDIR option. You can limit the maximal queue
## size using the SLOTS option (if omitted, the queue is limited by space
## available in the back end filesystem).
#
  set eventqueue
      basedir /var/lib/monit/events # set the base directory where events will be stored
      slots 100                     # optionally limit the queue size
#
#
## Send status and events to M/Monit (for more informations about M/Monit
## see http://mmonit.com/). By default Monit registers credentials with
## M/Monit so M/Monit can smoothly communicate back to Monit and you don't
## have to register Monit credentials manually in M/Monit. It is possible to
## disable credential registration using the commented out option below.
## Though, if safety is a concern we recommend instead using https when
## communicating with M/Monit and send credentials encrypted.
#
# set mmonit http://monit:monit@192.168.1.10:8080/collector
#     # and register without credentials     # Don't register credentials
#
#
## Monit by default uses the following format for alerts if the the mail-format
## statement is missing::
## --8<--
## set mail-format {
##      from: monit@$HOST
##   subject: monit alert --  $EVENT $SERVICE
##   message: $EVENT Service $SERVICE
##                 Date:        $DATE
##                 Action:      $ACTION
##                 Host:        $HOST
##                 Description: $DESCRIPTION
##
##            Your faithful employee,
##            Monit
## }
## --8<--
##
## You can override this message format or parts of it, such as subject
## or sender using the MAIL-FORMAT statement. Macros such as $DATE, etc.
## are expanded at runtime. For example, to override the sender, use:
#
# set mail-format { from: monit@foo.bar }
#
#
## You can set alert recipients whom will receive alerts if/when a
## service defined in this file has errors. Alerts may be restricted on
## events by using a filter as in the second example below.
#
# set alert sysadm@foo.bar                       # receive all alerts
# set alert manager@foo.bar only on { timeout }  # receive just service-
#                                                # timeout alert
#
#
## Monit has an embedded web server which can be used to view status of
## services monitored and manage services from a web interface. See the
## Monit Wiki if you want to enable SSL for the web server.
#
 set httpd port 2812 and
   use address 192.168.18.136
#    use address localhost  # only accept connection from localhost
#    allow localhost        # allow localhost to connect to the server and
    allow admin:monit      # require user 'admin' with password 'monit'
    allow @monit           # allow users of group 'monit' to connect (rw)
    allow @users readonly  # allow users of group 'users' to connect readonly
    allow 0.0.0.0/0.0.0.0
#
###############################################################################
## Services
###############################################################################
##
## Check general system resources such as load average, cpu and memory
## usage. Each test specifies a resource, conditions and the action to be
## performed should a test fail.
#
#  check system myhost.mydomain.tld
#    if loadavg (1min) > 4 then alert
#    if loadavg (5min) > 2 then alert
#    if memory usage > 75% then alert
#    if swap usage > 25% then alert
#    if cpu usage (user) > 70% then alert
#    if cpu usage (system) > 30% then alert
#    if cpu usage (wait) > 20% then alert
#
#   
## Check if a file exists, checksum, permissions, uid and gid. In addition
## to alert recipients in the global section, customized alert can be sent to
## additional recipients by specifying a local alert handler. The service may
## be grouped using the GROUP option. More than one group can be specified by
## repeating the 'group name' statement.
#   
#  check file apache_bin with path /usr/local/apache/bin/httpd
#    if failed checksum and
#       expect the sum 8f7f419955cefa0b33a2ba316cba3659 then unmonitor
#    if failed permission 755 then unmonitor
#    if failed uid root then unmonitor
#    if failed gid root then unmonitor
#    alert security@foo.bar on {
#           checksum, permission, uid, gid, unmonitor
#        } with the mail-format { subject: Alarm! }
#    group server
#
#   
## Check that a process is running, in this case Apache, and that it respond
## to HTTP and HTTPS requests. Check its resource usage such as cpu and memory,
## and number of children. If the process is not running, Monit will restart
## it by default. In case the service is restarted very often and the
## problem remains, it is possible to disable monitoring using the TIMEOUT
## statement. This service depends on another service (apache_bin) which
## is defined above.
#   
# check process apache with pidfile /usr/local/apache/logs/httpd.pid
#    start program = "/etc/init.d/httpd start" with timeout 60 seconds
#    stop program  = "/etc/init.d/httpd stop"
#    if cpu > 60% for 2 cycles then alert
#    if cpu > 80% for 5 cycles then restart
#    if totalmem > 200.0 MB for 5 cycles then restart
#    if children > 250 then restart
#    if loadavg(5min) greater than 10 for 8 cycles then stop
#    if failed host www.tildeslash.com port 80 protocol http
#       and request "/somefile.html"
#       then restart
#    if failed port 443 type tcpssl protocol http
#       with timeout 15 seconds
#       then restart
#    if 3 restarts within 5 cycles then timeout
#    depends on apache_bin
#    group server
#   
#monitoring httpd service check process apache2 with pidfile /var/run/apache2.pid start program = "/etc/init.d/apache2  start"
stop program = "/etc/init.d/apache2  stop"
#  if cpu > 80% for 5 cycles then restart
#    if totalmem > 200.0 MB for 5 cycles then restart
#    if children > 250 then restart
#    if loadavg(5min) greater than 10 for 8 cycles then stop
#    if failed host www.tildeslash.com port 80 protocol http
#       and request "/somefile.html"
#       then restart
   #if failed port 443 type tcpssl protocol http
   #    with timeout 15 seconds
   #    then restart
#    if failed host 192.168.137.6 port 2182 protocol http
#        with timeout 15 seconds
#        then restart
    if 3 restarts within 5 cycles then timeout
 #   depends on apache_bin
#     depends on apache2
#    group server    #Monitoring Mysql Service check process mysql with pidfile /var/run/mysqld/mysqld.pid
group database
start program = "/etc/init.d/mysql start"
stop program = "/etc/init.d/mysql stop"
if failed host 127.0.0.1 port 3306 then restart
if 5 restarts within 5 cycles then timeout
#if 5 restarts within 5 cycles then shutdown #Monitoring ssh Service check process sshd with pidfile /var/run/sshd.pid
group server
start program "/etc/init.d/ssh start"
stop program "/etc/init.d/ssh stop"
if failed port 22 protocol ssh then restart
if 5 restarts within 5 cycles then timeout #monit dhcpd check process dhcpd with pidfile  /run/dhcp-server/dhcpd.pid
group server
start program = "/usr/sbin/dhcpd -f -q -4 -pf /run/dhcp-server/dhcpd.pid -cf /etc/dhcp/dhcpd.conf"
stop program = "/usr/bin/killall dhcpd"
if failed port 67 type udp then restart
if 5 restarts within 5 cycles then  timeout
#monit iwndb
check process iwndb with MATCHING iwndb
group app
start program = "/iwncomm/ac/target/config/start_db.sh" as uid wlan and gid wlan  对于使用wlan账户安装，且需要调用动态库的应用进程，必须通过专门的脚本进行启动，脚本中需要指明动态库的环境变量，并且声明程序执行的uid和gid
#start program = "/bin/bash -c '/iwncomm/ac/target/config/start_db.sh &> /home/wlan/testdb.out'" as uid wlan and gid wlan可以通过这种启动方式将启动时的错误打印输出到指定文件
#start program = "/bin/bash -c '/iwncomm/ac/target/bin/iwndb  &> /home/wlan/iwndb.out'" as uid wlan and gid wlan
#start program = "/iwncomm/ac/target/bin/iwndb"
stop program = "/usr/bin/killall iwndb"杀掉所有iwndb进程
#if 3 restarts within 3 cycles then timeout
#if changed pid then  exec "/sbin/reboot now"针对关键进程重启的情况，设备复位
#if 2 restarts  within 3 cycles then exec "/sbin/reboot now"针对重启关键进程失败的情况，设备复位
#monit log
check process iwnlog  with MATCHING iwnlog
group app
start program = "/iwncomm/ac/target/bin/iwnlog" as uid wlan and gid wlan 对于使用wlan账户安装且不需要使用动态库的进程，直接启动
stop program = "/usr/bin/killall iwnlog"
#if changed pid then  exec "/sbin/reboot now" #if 2 restarts  within 3 cycles then exec "/sbin/reboot now"
if 2 restarts within 3 cycles then timeout
#depends on iwndb #monit dhcpCtrl
check process dhcpCtrl with MATCHING dhcpCtrl
group app
start program = "/iwncomm/ac/target/bin/dhcpCtrl" as uid wlan and gid wlan
stop program = "/usr/bin/killall dhcpCtrl"
#if 2 restarts  within 3 cycles then exec "/sbin/reboot now"
if 2 restarts within 3 cycles then timeout #monit wapi
check process wapi with MATCHING wapi
#group app
start program = "/iwncomm/ac/target/config/start_all.sh" as uid wlan and gid wlan
stop program = "/usr/bin/killall wapi"
#if 2 restarts  within 3 cycles then exec "/sbin/reboot now"
#if 2 restarts within 3 cycles then timeout ## Check filesystem permissions, uid, gid, space and inode usage. Other services,
## such as databases, may depend on this resource and an automatically graceful
## stop may be cascaded to them before the filesystem will become full and data
## lost.
#
#  check filesystem datafs with path /dev/sdb1
#    start program  = "/bin/mount /data"
#    stop program  = "/bin/umount /data"
#    if failed permission 660 then unmonitor
#    if failed uid root then unmonitor
#    if failed gid disk then unmonitor
#    if space usage > 80% for 5 times within 15 cycles then alert
#    if space usage > 99% then stop
#    if inode usage > 30000 then alert
#    if inode usage > 99% then stop
#    group server
#
#
## Check a file's timestamp. In this example, we test if a file is older
## than 15 minutes and assume something is wrong if its not updated. Also,
## if the file size exceed a given limit, execute a script
#
#  check file database with path /data/mydatabase.db
#    if failed permission 700 then alert
#    if failed uid data then alert
#    if failed gid data then alert
#    if timestamp > 15 minutes then alert
#    if size > 100 MB then exec "/my/cleanup/script" as uid dba and gid dba
#
#
## Check directory permission, uid and gid.  An event is triggered if the
## directory does not belong to the user with uid 0 and gid 0.  In addition,
## the permissions have to match the octal description of 755 (see chmod(1)).
#
#  check directory bin with path /bin
#    if failed permission 755 then unmonitor
#    if failed uid 0 then unmonitor
#    if failed gid 0 then unmonitor
#
#
## Check a remote host availability by issuing a ping test and check the
## content of a response from a web server. Up to three pings are sent and
## connection to a port and an application level network check is performed.
#
#  check host myserver with address 192.168.1.1
#    if failed icmp type echo count 3 with timeout 3 seconds then alert
#    if failed port 3306 protocol mysql with timeout 15 seconds then alert
#    if failed url http://user:password@www.foo.bar:8080/?querystring
#       and content == 'action="j_security_check"'
#       then alert
#
#
###############################################################################
## Includes
###############################################################################
##
## It is possible to include additional configuration parts from other files or
## directories.
#
   include /etc/monit/conf.d/*
#
保存退出后，执行monit -t 检查文件是否正确。 执行sudo /etc/init.d/monit start 和 sudo /etc/init.d/monit stop 启动和停止监控服务 方法3： 编写shell 脚本，实现周期运行，检测系统服务并安排重新启动。此方法未测试。