System Management Guide: Operating System and Devices

System Hang Management

System hang management allows users to run mission critical applications continuouly while improving application availablity. System hang detection alerts the system administrator of possible problems and then allows the administrator to log in as root or to reboot the system to resolve the problem.

shconf Script

The shconf command is invoked when System Hang Detection is enabled. shconf configures which events are surveyed and what actions are to be taken if such events occur.

The user can specify the five actions described below and can specify the priority level to check, the time out while no process or thread executes at a lower or equal priority, the terminal device for the warning action and the getty action:

• Log an error in errlog file
• Display a warning message on the system console (alphanumeric console) or on a specified TTY
• Reboot the system
• Give a special getty to allow the user to log in as root and launch commands
• Launch a command

For the Launch a command and Give a special getty options, SHD will launch the special getty or the specified command at the highest priority. The special getty will print a warning message specifying that it is a recovering getty running at priority 0. The following table lists the default values when the SHD is enabled. Only one action is enabled per type of detection.

Note : When Launch a recovering getty on a console is enabled, the shconf script adds the -u flag to the getty line in the inittab that is associated with the console login.

shdaemon is a process launched by init. It is in charge of handling the detection of system hang. It retrieves configuration information, initiates working structures, and starts detection times set in by the user.

shdaemon runs at priority 0 (zero).

SMIT Interface

You can manage the SHD configuration from the SMIT System Environments menu. From the System Environments menu, select Change / Show Characteristics of Operating System, then System Hang Detection. The options in this menu allow system administrators to enable or disable the detection mechanism.

The Manage System Hang Detection menu contains the following items:

• System Hang Detection Status
• Change / Show Current Configuration for Priority Problem Detection

System Hang Detection Status

The System Hang Detection Status menu displays the current state (enable or disable) of the SHD feature. The only change that can be made from this option is either to enable or disable system hang detection.

Change / Show Current Configuration for Priority Problem Detection

The Change / Show Current Configuration for Priority Problem Detection menu displays the current time-out and the process priority for each action:

Log an Error in the Error Log                [disable]
    Detection Time-out                       [120]
    Process Priority                         [60]
 
Display a warning message on a console       [disable]
    Detection Time-out                       [120]
    Process Priority                         [60]
    Terminal Device                          [console]  
 
Launch a recovering getty on a console       [enable]
    Detection Time-out                       [120]
    Process Priority                         [60]
    Terminal Device                          [console]
 
Launch a command                             [disable]
    Detection Time-out                       [120]
    Process Priority                         [60]
    Script                                   [ ]
 
Automatically REBOOT system after Detection  [disable]
    Detection Time-out                       [300]
    Process Priority                         [39]