Limits on the consumption of system resources by the current process
and each process it creates may be obtained with the
getrlimit ();
system call, and set with the
setrlimit ();
system call.
The
Fa resource
argument is one of the following:
RLIMIT_AS
The maximum amount (in bytes) of virtual memory the process is
allowed to map.
RLIMIT_CORE
The largest size (in bytes)
core(5)
file that may be created.
RLIMIT_CPU
The maximum amount of cpu time (in seconds) to be used by
each process.
RLIMIT_DATA
The maximum size (in bytes) of the data segment for a process;
this defines how far a program may extend its break with the
sbrk(2)
function.
RLIMIT_FSIZE
The largest size (in bytes) file that may be created.
RLIMIT_MEMLOCK
The maximum size (in bytes) which a process may lock into memory
using the
mlock(2)
system call.
RLIMIT_NOFILE
The maximum number of open files for this process.
RLIMIT_NPROC
The maximum number of simultaneous processes for this user id.
RLIMIT_RSS
The maximum size (in bytes) to which a process's resident set size may
grow.
This imposes a limit on the amount of physical memory to be given to
a process; if memory is tight, the system will prefer to take memory
from processes that are exceeding their declared resident set size.
RLIMIT_SBSIZE
The maximum size (in bytes) of socket buffer usage for this user.
This limits the amount of network memory, and hence the amount of
mbufs, that this user may hold at any time.
RLIMIT_STACK
The maximum size (in bytes) of the stack segment for a process;
this defines how far a program's stack segment may be extended.
Stack extension is performed automatically by the system.
A resource limit is specified as a soft limit and a hard limit.
When a
soft limit is exceeded a process may receive a signal (for example, if
the cpu time or file size is exceeded), but it will be allowed to
continue execution until it reaches the hard limit (or modifies
its resource limit).
The
Vt rlimit
structure is used to specify the hard and soft limits on a resource,
struct rlimit {
rlim_t rlim_cur; /* current (soft) limit */
rlim_t rlim_max; /* maximum value for rlim_cur */
};
Only the super-user may raise the maximum limits.
Other users
may only alter
Fa rlim_cur
within the range from 0 to
Fa rlim_max
or (irreversibly) lower
Fa rlim_max .
An
``infinite''
value for a limit is defined as
RLIM_INFINITY
Because this information is stored in the per-process information,
this system call must be executed directly by the shell if it
is to affect all future processes created by the shell;
limit
is thus a built-in command to
csh(1).
The system refuses to extend the data or stack space when the limits
would be exceeded in the normal way: a
brk(2)
function fails if the data space limit is reached.
When the stack limit is reached, the process receives
a segmentation fault
(SIGSEGV
)
if this signal is not
caught by a handler using the signal stack, this signal
will kill the process.
A file I/O operation that would create a file larger that the process'
soft limit will cause the write to fail and a signal
SIGXFSZ
to be
generated; this normally terminates the process, but may be caught.
When
the soft cpu time limit is exceeded, a signal
SIGXCPU
is sent to the
offending process.
RETURN VALUES
Rv -std
ERRORS
The
getrlimit ();
and
setrlimit ();
system calls
will fail if:
Bq Er EFAULT
The address specified for
Fa rlp
is invalid.
Bq Er EPERM
The limit specified to
setrlimit ();
would have
raised the maximum limit value, and the caller is not the super-user.
