Go to main content

Oracle® Solaris 11.4 Tunable Parameters Reference Manual

Exit Print View

Updated: January 2019
 
 

Process-Sizing Parameters

Several parameters (or variables) are used to control the number of processes that are available on the system and the number of processes that an individual user can create. The foundation parameter is maxusers. This parameter drives the values assigned to max_nprocs and maxuprc.

max_nprocs Parameter

Description

Specifies the maximum number of processes that can be created on a system. Includes system processes and user processes. Any value specified in /etc/system.dfile is used in the computation of maxuprc.

This value is also used in determining the size of several other system data structures. Other data structures where this parameter plays a role are as follows:

  • Determining the size of the directory name lookup cache (if ncsize is not specified)

  • Verifying that the amount of memory used by configured system V semaphores does not exceed system limits

  • Configuring Hardware Address Translation resources for x86 platforms

Data Type

Signed integer

Default

10 + (16 x maxusers) if maxusers is set in /etc/system.d/file

The larger of 30,000 or 10 + (128 x number of CPUs), if maxusers is not set in /etc/system.d/file

Range

26 to value of maxpid

Dynamic?

No

Validation

Yes. If the value exceeds maxpid, it is set to maxpid .

When to Change

Changing this parameter is one of the steps necessary to enable support for more than 30,000 processes on a system.

Commitment Level

Unstable

maxuprc Parameter

Description

Specifies the maximum number of processes that can be created on a system by any one user.

Data Type

Signed integer

Default

max_nprocs - reserved_procs

Range

1 to max_nprocs - reserved_procs

Units

Processes

Dynamic?

No

Validation

Yes. This value is compared to max_nprocs - reserved_procs and set to the smaller of the two values.

When to Change

When you want to specify a hard limit for the number of processes a user can create that is less than the default value of however many processes the system can create. Attempting to exceed this limit generates the following warning messages on the console or in the messages file:

out of per-user processes for uid N
Commitment Level

Unstable

maxusers Parameter

Description

Originally, maxusers defined the number of logged in users the system could support. When a kernel was generated, various tables were sized based on this setting. Current Oracle Solaris releases do much of its sizing based on the amount of memory on the system. Thus, much of the past use of maxusers has changed. The following list identifies subsystems that are still derived from maxusers:

  • The maximum number of processes on the system

  • The number of quota structures held in the system

  • The size of the directory name look-up cache (DNLC)

Data Type

Signed integer

Default

Lesser of the amount of memory in MB or 2048, and the greater of that value and nCPUs x 8

Range

1 to the greater of 2048 or nCPUs x 8, based on the size of physical memory, if not set in /etc/system.d/file

1 to the greater of 4096 or the nCPUs x 8, if set in /etc/system.d/file

Units

Users

Dynamic?

No. After computation of dependent parameters is done, maxusers is never referenced again.

Validation

If the value is greater than the maximum allowed, it is reset to the maximum. A message to that effect is displayed.

When to Change

When the default number of user processes derived by the system is too low. This situation is evident when the following message displays on the system console:

out of processes

You might also change this parameter when the default number of processes is too high, as in these situations:

  • Database servers that have a lot of memory and relatively few running processes can save system memory when the default value of maxusers is reduced.

  • If file servers have a lot of memory and few running processes, you might reduce this value. However, you should explicitly set the size of the DNLC. See ncsize Parameter.

Commitment Level

Unstable

ngroups_max Parameter

Description

Specifies the maximum number of supplemental groups per process.

Data Type

Signed integer

Default

1024

Range

16 to 1024

Units

Groups

Dynamic?

No

Validation

Yes. If ngroups_max is set to an invalid value, it is automatically reset to the closest legal value. For example, if it is set to less than zero, it is reset to 0. If it is set to greater than 1024, it is reset to 1024.

When to Change

Review the following considerations if you are using NFS AUTH_SYS authentication and you want to increase the default ngroups_max value:

  1. If ngroups_max is set to 16 or if the NFS client's AUTH_SYS credential that is provided has 15 or fewer groups, the client's group information is used.

  2. If ngroups_max is set to greater than 16 and the NFS client's AUTH_SYS credential from the name server contains exactly 16 groups, the maximum allowed, the NFS server consults the name server and matches the client's UID to a user name. Then, the name server computes a list of groups to which the user belongs.

Commitment Level

Unstable

pidmax Parameter

Description

Specifies the value of the largest possible process ID.

pidmax sets the value for the maxpid variable. Once maxpid is set, pidmax is ignored. maxpid is used elsewhere in the kernel to determine the maximum process ID and for validation checking.

Any attempts to set maxpid by adding an entry to a file in the /etc/system.d directory have no effect.

Data Type

Signed integer

Default

30,000

Range

5 to 999,999

Units

Processes

Dynamic?

No. Used only at boot time to set the value of pidmax.

Validation

Yes. Value is compared to the value of reserved_procs and 999,999. If less than reserved_procs or greater than 999,999, the value is set to 999,999.

Implicit

max_nprocs range checking ensures that max_nprocs is always less than or equal to this value.

When to Change

Required to enable support for more than 30,000 processes on a system. See also max_nprocs Parameter.

Commitment Level

Unstable

reserved_procs Parameter

Description

Specifies the number of system process slots to be reserved in the process table for processes with a UID of root (0). For example, fsflush has a UID of root (0).

Data Type

Signed integer

Default

5

Range

5 to MAXINT

Units

Processes

Dynamic?

No. Not used after the initial parameter computation.

Validation

Any /etc/system.d/file setting is honored.

Commitment Level

Unstable

When to Change

Consider increasing to 10 + the normal number of UID 0 (root) processes on system. This setting provides some cushion should it be necessary to obtain a root shell when the system is otherwise unable to create user-level processes.