Unix Advanced [Electronic resources] نسخه متنی

Controlling Services

To live with services that run all the time (as opposed to the ones that are started when necessary by a super-server that monitors network ports (such as inetd and xinetd), you'll need to know how to start and stop them without rebooting the system. Reboots mean downtime, and that's not a good thing in the server world.

Code listing 5.1. Using the find command to look for xinetd's startup script.

[chrish@dhcppc0 ~]$ cd /etc/rc.d/init.d
[chrish@dhcppc0 init.d]$ find . -name 
\*inetd\*
./xinetd

Code listing 5.2. Searching for inetd's startup script on FreeBSD.

freebsd# cd /etc/rc.d
freebsd# find . -name    \*inetd\*
./inetd

To find a service's control script

If a service has a control script, it will be installed in the standard startup-script directory, along with the service's configuration scripts, or with the service's program itself.

Code listing 5.3. Looking for startup scripts on Mac OS X can be more of a challenge, because the names have changed slightly.

bender:~ chrish$ cd /System/Library/StartupItems
bender:/System/Library/StartupItems chrish$ ls
AMD            CoreGraphics        LoginWindow         Postfix
Accounting     CrashReporter       NFS                 PrintingServices
Apache         Cron                NIS                 RemoteDesktopAgent
AppServices    DirectoryServices   NetInfo             SNMP
AppleShare     Disks               Network             SecurityServer
AuthServer     IPServices          NetworkExtensions   SystemLog
BIND           KernelEventAgent    NetworkTime         SystemTuning
ConfigServer   LDAP                Portmap             DNSResponder
bender:/System/Library/StartupItems chrish$ find . -name \*Log\*
./LoginWindow
./LoginWindow/LoginWindow
./SystemLog
./SystemLog/SystemLog

To stop a running service

Stopping a running service depends on how it was started.

• If the service has a startup script, run the script with the stop argument:

  
  /path/to/startup_script stop
  

• If the service uses its own control script (you'll find out about this in the service's man pages), follow the instructions in the service's man pages. They usually have a stop script, or a script that accepts a stop or exit argument.

• If you can't find any information about cleanly stopping a service and you really need it to stop, use the kill command to send it a terminate signal:

  
  kill -TERM pid
  

  How do you find the process ID, pid? Using ps and grep (Code Listing 5.4):

  
  ps -ax | grep service_name
  

  The first column of the output is the PID, and you can ignore the line with your grep command in it.

• Some systems (including Fedora Core and FreeBSD) have a pkill command that will kill a process by name:

  
  pkill -TERM ntpd
  

• Fedora Core and Mac OS X have a service command, which will send a command to the named service:

  
  service ntpd stop
  

Code listing 5.4. Using the ps command and grep to find the process ID of the NTP daemon.

bender:~ chrish$ ps ax | grep ntpd
321  ??  Ss     0:00.14 ntpd -f
/var/run/ntp.drift -p /var/run/ntpd.pid
647 std  R+     0:00.00 grep ntpd
bender:~ chrish$

To start a service

Starting a service depends on whether it has a startup script.

• If the service has a startup script, run the script with the start argument:

  
  /path/to/startup_script start
  

• If the service uses its own control script (you'll find out about this in the service's man pages), follow the instructions in the service's man pages. They usually have a start script, or a script that accepts a start or run argument.

• If you can't find any information about properly starting a service, you can probably run it directly from the command line:

  
  /path/to/service &
  

  Check the service's man pages for a -d or -D option (usually marked "run as daemon" in the documents) and any other useful arguments you might need to include.

To restart a running service

There are two ways to restart a running service.

• kill -HUP service_pid

  Sending the HUP signal to a service usually tells it to reload its configuration and restart. I say "usually" because this is only a convention, not a requirement. Check the man page for your service to be sure. You can generally find the service_pid using the ps command and less or grep. You might also find the service's program ID in /var/run/service.pid.

• /path/to/startup scripts/service_script restart

  Modern Unix systems all use scripts to launch services during system startup (see Chapter 2), and the restart option will restart a running service. If restart isn't supported on your system, use stop and then start to have the same effect.

Tips

• Fedora Core has a nice graphical service editing tool created by Red Hat, the Service Configuration tool (Figure 5.1). You can start this by going to the Applications menu in the top left of the screen and choosing System Settings > Server Settings > Services.

  Figure 5.1. Red Hat's Service Configuration tool lets you modify the running services using a graphical interface.

  
  

  

• If you've installed a Cygwin daemon as a Windows service (using the cygrunsrv command), you can use the Services item in the Administrative Tools folder of Control Panel (Figure 5.2). Scroll down the list until you find the service you're interested in, then right-click it and choose your desired action from the contextual pop-up menu.

  Figure 5.2. The Services control panel application under Windows lets you control the myriad services installed on a modern Windows system.

  
  

  [View full size image]

  

• Mac OS X services can mostly be controlled through the Sharing pane of System Preferences (Figure 5.3). Simply select the desired service, and then click the Start/Stop button.

  Figure 5.3. The Sharing pane in the Mac OS X System Preferences controls several standard Internet services.

  
  

  

• Need to kill multiple copies of a process? Try this:

  
  ps ax | grep process_name |
   awk -e '{ print $1; }' |
   xargs -n 1 kill -TERM
  

  This ps command lists all of the processes currently running on your system. grep then picks out the ones that match process_name, and awk takes those and prints only the process IDs. The xargs command takes those PIDs and fires off one kill -TERM command per PID to tell each instance of the service to exit.

• For a pesky service that won't exit with the TERM signal, use KILL instead. The advantage of using TERM is that it gives the program a chance to clean up after itself. With KILL, it just exits immediately.