sysctl -- get or set kernel state

retrieves kernel state and allows processes to set kernel state.
The state to be retrieved or set is described using a Management Information Base (MIB) style name, described as a dotted set of components.

-a	List all the currently available non-opaque values. Ignored if one or more variable names are specified on the command line.
-A	List ALL MIB variables including opaque variables (which are normally suppressed). format and length are displayed, as well as a hex dump of the first 16 bytes. Produces identical output to -a El Captian 4/15/16 Differeces in Mac OS High Sierra.
-X	displays hex dump user.cs_path: /usr/bin:/bin:/usr/sbin:/sbin user.bc_base_max: 0x00000063 user.bc_dim_max: 0x00000800 user.bc_scale_max: 0x00000063 …
-b	Output in binary, value only (direct output to file)
-n	Show only values, not names. Useful for setting shell variables. For example, to save the pagesize in variable $psize: set psize=`sysctl -n hw.pagesize`
-w name=value	Sets values.

If just a MIB style name is given, the corresponding value is retrieved.

The information available from sysctl consists of integers, strings, and tables.
The tabular information can only be retrieved by special programs such as ps, systat, and netstat.

Name Type Changable kern.ostype string no kern.osrelease string no kern.osrevision integer no kern.version string no kern.maxvnodes integer yes kern.maxproc integer yes kern.maxfiles integer yes kern.argmax integer no kern.securelevel integer raise only kern.hostname string yes kern.hostid integer yes kern.clockrate struct no kern.posix1version integer no kern.ngroups integer no kern.job_control integer no kern.saved_ids integer no kern.link_max integer no kern.max_canon integer no kern.max_input integer no kern.name_max integer no kern.path_max integer no kern.pipe_buf integer no kern.chown_restricted integer no kern.no_trunc integer no kern.vdisable integer no kern.boottime struct no

Name Type Changable vm.loadavg struct no vm.swapusage struct no machdep.console_device dev_t no net.inet.ip.forwarding integer yes net.inet.ip.redirect integer yes net.inet.ip.ttl integer yes net.inet.icmp.maskrepl integer yes net.inet.udp.checksum integer yes hw.machine string no hw.model string no hw.ncpu integer no hw.byteorder integer no hw.physmem integer no hw.usermem integer no hw.memsize integer no hw.pagesize integer no

Name Type Changable user.cs_path string no user.bc_base_max integer no user.bc_dim_max integer no user.bc_scale_max integer no user.bc_string_max integer no user.coll_weights_max integer no user.expr_nest_max integer no user.line_max integer no user.re_dup_max integer no user.posix2_version integer no user.posix2_c_bind integer no user.posix2_c_dev integer no user.posix2_char_term integer no user.posix2_fort_dev integer no user.posix2_fort_run integer no user.posix2_localedef integer no user.posix2_sw_dev integer no user.posix2_upe integer no

sysctl can get or set debugging variables that have been identified for its display.

sysctl debug

debug.lowpri_throttle_max_iosize: 131072
debug.lowpri_throttle_tier1_window_msecs: 25
debug.lowpri_throttle_tier2_window_msecs: 100
debug.lowpri_throttle_tier3_window_msecs: 500
debug.lowpri_throttle_tier1_io_period_msecs: 15
debug.lowpri_throttle_tier2_io_period_msecs: 50
debug.lowpri_throttle_tier3_io_period_msecs: 200
debug.lowpri_throttle_tier1_io_period_ssd_msecs: 5
debug.lowpri_throttle_tier2_io_period_ssd_msecs: 15
debug.lowpri_throttle_tier3_io_period_ssd_msecs: 25
debug.lowpri_throttle_enabled: 1

debug.bpf_bufsize:      4096
debug.bpf_maxbufsize: 524288
debug.bpf_maxdevices:    256
debug.bpf_wantpktap: 0
debug.bpf_debug: 0

debug.sched: 0
debug.toggle_address_reuse: 0
debug.sys_override_enabled: 1
debug.kextlog: 4083
debug.swd_kext_name: 
debug.swd_delay_type: 
debug.swd_delay_duration: 0

debug.iokit: 0
debug.iotrace: 0
debug.darkwake: 3
debug.noidle: 0
debug.wdtlog: 95013m1/095033m1/095053m1/095073m1/
095093m1/095113m1/095133m1/095153m1/095173m1/095193m1/
095213m1/095233m1/095253m1/095273m1/095293m1/095313m1/
095333m1/095353m1/095374m1/095394m1/095414m1/095434m1/
095454m1/095474m1/095494m1/095514m1/095534m1/095554m1/
095574m1/095594m1/095634m1/095654m1/0

sysctl vfs

EXAMPLES

Maximum number of processes allowed in the system: sysctl kern.maxproc

clock rate : sysctl kern.clockrate

load average history : sysctl vm.loadavg

swap space usage : sysctl vm.swapusage

Set the maximum number of processes allowed in the system to 1000: sysctl -w kern.maxproc=1000

Linux sudo sysctl vm

vm.admin_reserve_kbytes = 8192 vm.block_dump = 0 vm.compact_unevictable_allowed = 1 vm.dirty_background_bytes = 0 vm.dirty_background_ratio = 10 vm.dirty_bytes = 0 vm.dirty_ratio = 20 vm.dirty_expire_centisecs = 3000 vm.dirty_writeback_centisecs = 500 vm.dirtytime_expire_seconds = 43200	vm.drop_caches = 0 vm.extfrag_threshold = 500 vm.laptop_mode = 0 vm.legacy_va_layout = 0 vm.lowmem_reserve_ratio = 32 vm.max_map_count = 65530 vm.min_free_kbytes = 16384 vm.mmap_min_addr = 4096 vm.mmap_rnd_bits = 8 vm.nr_pdflush_threads = 0	vm.oom_dump_tasks = 1 vm.oom_kill_allocating_task = 0 vm.overcommit_kbytes = 0 vm.overcommit_memory = 0 vm.overcommit_ratio = 50 vm.page-cluster = 3 vm.panic_on_oom = 0 vm.percpu_pagelist_fraction = 0 vm.swappiness = 10 vm.user_reserve_kbytes = 13770 vm.vfs_cache_pressure = 100 vm.watermark_scale_factor = 10
Show cat /proc/vmstat | egrep "dirty|writeback" nr_dirty 878 pages waiting nr_writeback 0 nr_writeback_temp 0

FILES

<sys/sysctl.h> top level identifiers, second level kernel and hardware identifiers, and user level identifiers
<sys/socket.h> second level network identifiers
<sys/gmon.h> third level profiling identifiers
<vm/vm_param.h> second level virtual memory identifiers
<netinet/in.h> third level Internet identifiers and fourth level IP identifiers
<netinet/icmp_var.h> fourth level ICMP identifiers
<netinet/udp_var.h> fourth level UDP identifiers

SEE ALSO

For a detailed description of these variable see sysctl(3).