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Manual Pages  — RCTL


rctl – display and update resource limits database



rctl [-h] [-n] [filter ...]
rctl -a rule ...
rctl -l [-h] [-n] filter ...
rctl -r filter ...
rctl -u [-h] filter ...


When called without options, the rctl command writes currently defined RCTL rules to standard output.

If a filter argument is specified, only rules matching the filter are displayed. The options are as follows:
-a rule
  Add rule to the RCTL database.
-l filter
  Display rules applicable to the process defined by filter. Note that this is different from showing the rules when called without any options, as it shows not just the rules with subject equal to that of process, but also rules for the user, jail, and login class applicable to the process.
-r filter
  Remove rules matching filter from the RCTL database.
-u filter
  Display resource utilization for a subject ( process, user, loginclass or jail ) matching the filter.
  "Human-readable" output. Use unit suffixes: Byte, Kilobyte, Megabyte, Gigabyte, Terabyte and Petabyte.
  Display user IDs numerically rather than converting them to a user name.

Modifying rules affects all currently running and future processes matching the rule.


Syntax for a rule is subject:subject-id:resource:action=amount/per.

subject defines the kind of entity the rule applies to. It can be either process, user, loginclass, or jail.
  identifies the subject. It can be a process ID, user name, numerical user ID, login class name from login.conf(5), or jail name.
resource identifies the resource the rule controls. See the RESOURCES section below for details.
action defines what will happen when a process exceeds the allowed amount. See the ACTIONS section below for details.
amount defines how much of the resource a process can use before the defined action triggers. Resources which limit bytes may use prefixes from expand_number(3).
per defines what entity the amount gets accounted for. For example, rule "loginclass:users:vmemoryuse:deny=100M/process" means that each process of any user belonging to login class "users" may allocate up to 100MB of virtual memory. Rule "loginclass:users:vmemoryuse:deny=100M/user" would mean that for each user belonging to the login class "users", the sum of virtual memory allocated by all the processes of that user will not exceed 100MB. Rule "loginclass:users:vmemoryuse:deny=100M/loginclass" would mean that the sum of virtual memory allocated by all processes of all users belonging to that login class will not exceed 100MB.

A valid rule has all those fields specified, except for per, which defaults to the value of subject.

A filter is a rule for which one of more fields other than per is left empty. For example, a filter that matches every rule could be written as ":::=/", or, in short, ":". A filter that matches all the login classes would be "loginclass:". A filter that matches all defined rules for maxproc resource would be "::maxproc".


process numerical Process ID
user user name or numerical User ID
loginclass login class fromlogin.conf(5)
jail jail name


cputime CPU time, in seconds
datasize data size, in bytes
stacksize stack size, in bytes
coredumpsize core dump size, in bytes
memoryuse resident set size, in bytes
memorylocked locked memory, in bytes
maxproc number of processes
openfiles file descriptor table size
vmemoryuse address space limit, in bytes
pseudoterminals number of PTYs
swapuse swap space that may be reserved or used, in bytes
nthr number of threads
msgqqueued number of queued SysV messages
msgqsize SysV message queue size, in bytes
nmsgq number of SysV message queues
nsem number of SysV semaphores
nsemop number of SysV semaphores modified in a single semop(2) call
nshm number of SysV shared memory segments
shmsize SysV shared memory size, in bytes
wallclock wallclock time, in seconds
pcpu %CPU, in percents of a single CPU core
readbps filesystem reads, in bytes per second
writebps filesystem writes, in bytes per second
readiops filesystem reads, in operations per second
writeiops filesystem writes, in operations per second


deny deny the allocation; not supported for cputime, wallclock, readbps, writebps, readiops, and writeiops
log log a warning to the console
devctl send notification todevd(8) using system = "RCTL", subsystem = "rule", type = "matched"

e.g. sigterm; send a signal to the offending process. See signal(3) for a list of supported signals
throttle slow down process execution; only supported for readbps, writebps, readiops, and writeiops.

Not all actions are supported for all resources. Attempting to add a rule with an action not supported by a given resource will result in error.


The utility exits 0 on success, and >0 if an error occurs.


Prevent user "joe" from allocating more than 1GB of virtual memory:


Remove all RCTL rules:


Display resource utilization information for jail named "www":


Display all the rules applicable to process with PID 512:


Display all rules:


Display all rules matching user "joe":


Display all rules matching login classes:



cpuset(1), rctl(4), rctl.conf(5)


The rctl command appeared in FreeBSD 9.0 .


The rctl was developed by Edward Tomasz Napierala <Mt trasz@FreeBSD.org> under sponsorship from the FreeBSD Foundation.


Limiting memoryuse may kill the machine due to thrashing.

The readiops and writeiops counters are only approximations. Like readbps and writebps, they are calculated in the filesystem layer, where it is difficult or even impossible to observe actual disk device operations.

The writebps and writeiops resources generally account for writes to the filesystem cache, not to actual devices.

RCTL (8) February 26, 2018

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