Overview of Kernel Tunable Parameters

Overview of Kernel Tunable Parameters

Tunable parameters control characteristics of processes, files, and system activity. They set various table sizes and system thresholds to handle the expected system load. If certain system structures are too large, they waste memory space that would otherwise be used for other processes and can increase system overhead due to lengthy table searches. If they are set too low, they can cause excessive I/O, process aborts, or even a system crash, depending on the particular parameter.

This section briefly introduces some of the tunable parameters and switches. Appendix A, "IRIX Kernel Tunable Parameters," describes all parameters, gives default values, provides suggestions on when to change each parameter, and describes problems you may encounter.

The Types of Parameters

Tunable parameters are specified in separate configuration files in the /var/sysgen/mtune and the /var/sysgen/master.d directories. See the mtune(4) reference page for mtune information and the master(4) reference page for information on master.d.

The default values for the tunable parameters are usually acceptable for most configurations for a single-user workstation environment. However, if you have a lot of memory or your environment has special needs, you may want to adjust the size of a parameter to meet those needs. A few of the parameters you may want to adjust are listed below.

nproc: defines the maximum number of processes, system-wide. This parameter is typically auto-configured.
maxup: defines the maximum number of processes per UID.
rlimit-core-cur: the maximum size of a core file.
rlimit-data-cur: the maximum amount of data space available to a process.
rlimit-fsize-cur: the maximum file size available to a process.
rlimit-nofile-cur: the maximum number of file descriptors available to a process.
rlimit-rss-cur: the maximum resident set size available to a process.
rlimit-vmem-cur: the maximum amount of mapped memory for a process.
sshmseg: specifies the maximum number of attached shared memory segments per process.