Understanding the System Resource Controller (SRC) in AIX

For anyone working with AIX, the System Resource Controller (SRC) is an essential tool. Think of it as a facilitator that helps system admins and users to manage and oversee different processes and programs more efficiently. Let’s break this down:

What’s a Subsystem? Imagine a software module that can operate on its own or as part of a larger system. That’s a subsystem. Its primary role? To perform a specific function. Think of it as a unit of a program that does a particular job.

Features of SRC:

1. It oversees related programs that come together to do a specific task.
2. These programs can further be broken down into ‘subservers’, commonly known as daemons.
3. The SRC manages these subsystems and their daemons, organizing them into groups for better control.
4. With SRC, you can start, stop, monitor, and update these subsystems and daemons easily.
5. And here’s a fun fact: When you boot up your system, SRC starts automatically. This is thanks to an entry for /usr/bin/srcmstr daemon in the /etc/inittab file.

Understanding SRC’s Components:

• Subserver: These are individual programs or processes that belong to a subsystem. Examples include sshd and ftpd.
• Subsystem: This is like a container that holds multiple subservers. Its job is to start, stop, and monitor them. Some examples are gated, inetd, and named.
• Subsystem Group: When you group multiple subsystems under one umbrella, you get a subsystem group. This makes it easy to control them all at once. For instance, groups like TCP/IP, Network Information System (NIS), and Network File Systems (NFS) are such examples.

To visualize, imagine a group called “tcp/ip”. Under it, there’s a subsystem named “inetd”. Within this subsystem, there’s a subserver or daemon known as “ftp”.

SRC Commands at a Glance:

• Operational Commands:
  • srcmstr: Initiates the SRC.
  • startsrc: Fires up a subsystem, group, or subserver.
  • stopsrc: Halts the aforementioned elements.
  • refresh: Updates a subsystem.
  • traceson & tracesoff: Turns tracking for a subsystem or subserver on or off.
  • lssrc: Checks a subsystem’s status.
• Examples of Command Usage:
  • lssrc -a: View the status of all subsystems.
  • startsrc -s inetd: Get inetd subsystem running.
  • stopsrc -g tcpip: Stop the tcpip subsystem group.
  • kill [PID of process]: End a process not initiated by srcmstr.
• Configuration Commands:
  • mkssy: Sets up a new subsystem.
  • chssys: Modify parameters of an existing subsystem.
  • rmssys: Deletes a subsystem.

# mkssys -p /usr/sbin/sshd \   /* Absolute path to the subsystem executable
                                  program. */
         -s sshd_adm \         /* Name that uniquely identifies the subsys. */
         -u 0 \                /* User id for the subsystem. */
         -a "-D -f /etc/ssh/sshd_config_adm" \   /* Arguments that must be
                                                    passed to the command. */
         -e /dev/console \     /* Where the subsystem standard error data is
                                  placed. */
         -i /dev/console \     /* Where the subsys. standard input is routed. */
         -o /dev/console \     /* Where the subsys. standard output is placed. */
         -R \                  /* Subsystem is restarted if the subsystem stops
                                  abnormally. */
         -Q \                  /* Multiple instances of the subsystem are not
                                  allowed to run at the same time. */
         -S \                  /* Subsystem uses the signals communication
                                  method. */
         -f 9 \                /* Signal sent to the subsystem when a forced
                                  stop of the subsystem is requested. */
         -n 15 \               /* Signal sent to the subsystem when a normal
                                  stop of the subsystem is requested. */
         -E 20 \               /* Execution priority of the subsystem. */
         -G ssh \              /* Subsystem belongs to the group specified. */
         -d \                  /* Inactive subsystems are displayed when the
                                  lssrc -a command request is made. */
         -w 20                 /* Time, in seconds, allowed to elapse between a
                                  stop cancel (SIGTERM) signal and a subsequent
                                  SIGKILL signal. */
Check the service's configuration:

# lssrc -S -s sshd_adm                
#subsysname:synonym:cmdargs:path:uid:auditid:standin:standout:standerr:action:multi:contact:svrkey:svrmtype:\
 priority:signorm:sigforce:display:waittime:grpname:
sshd_adm::-D -f /etc/ssh/sshd_config_adm:/usr/sbin/sshd:0:0:/dev/console:/dev/console:/dev/console:-R:-Q:-S:0:0:\
30:25:9:-d:20:ssh:

# odmget -q subsysname=sshd_adm SRCsubsys

SRCsubsys:
        subsysname = "sshd_adm"
        synonym = ""
        cmdargs = "-D -f /etc/ssh/sshd_config_adm"
        path = "/usr/sbin/sshd"
        uid = 0
        auditid = 0
        standin = "/dev/console"
        standout = "/dev/console"
        standerr = "/dev/console"
        action = 1
        multi = 0
        contact = 2
        svrkey = 0
        svrmtype = 0
        priority = 20
        signorm = 15
        sigforce = 9
        display = 1
        waittime = 20
        grpname = "ssh"