Monitoring use of system resources

z/OS UNIX provides the system programmer with a number of controls that monitor and tune the use of system resources by users. As part of the tuning process, you can follow these initial rules of thumb:

Assume that each user will consume up to double the system resources required for a TSO/E user.
Assume that at most 4 PTYs will be required per average user.
Assume that the starting point for maximum processes per user is 25.
Assume that 4 concurrent processes will be required by the average active user.
Assume that 5 processes will be required for various daemons.
Assume that 3 concurrent address spaces will be required by the average active user. This number will be high if your users are running with the _BPX_SHAREAS environment variable set to YES.
Assume that no user, including servers or daemons, needs more than 2048 files open at one time for Unicode Services conversion. In this case, the default MAXIOBFUSER setting of 2048 (which equals 2 G of above the bar storage) is enough and no changes to the initial setting is necessary.

Tip: If you have a few users who need a large number of processes, use the PROCUSERMAX keyword in the OMVS segment to set the process limit for these users.

For example, assume that your system supports 600 TSO/E users and has enough capacity for 20 additional users. Rather than adding more TSO/E work, you want to allow TSO/E users to access z/OS UNIX. You have no other z/OS UNIX work on your system at this time. In this example the initial settings in BPXPRMxx might be:

MAXUIDS(20)
MAXPTYS(80)
MAXPROCUSER(25)
MAXPROCSYS(85)

Table 1 shows how the initial settings were calculated.

Table 1. Calculating initial settings when tuning process activity. This table lists the initial settings for certain BPXPRMxx parameters.
Parameter	Initial setting	Note
MAXUIDS	20	If you allow 20 current TSO/E users to access the z/OS UNIX system, each of them could consume twice the resource they normally used for TSO/E. This would require all your remaining system resources.
MAXPTYS	80	Assume that 4 PTYs are needed per user. Users can login with multiple sessions at the same time
MAXPROCUSER	25	This should normally be a reasonable starting point. Some users might require more processes, depending on the work they are doing. This value can be set only on a system-wide basis.
MAXPROCSYS	85	Assume that you need 4 processes per user and 5 processes for daemons. (20 users * 4) + 5 daemons = 85 processes.