ulimit 1 user commands nosh ulimit change resource limit then chain ulimit -H -S limits next-prog Most shells have a built-in ulimit command that does not chain and that has additional interactive functionality. See the manual for each individual shell for its built-in command. This command is more commonly used with exec1 and nosh1. Whilst it is built in to them, it is an external command as far as shells are concerned. ulimit is a chain-loading utility that changes its resource limits and then chain loads to next-prog with the execvp3 function. next-prog may contain its own command line options, which ulimit will ignore. If the -H command line option is used, ulimit will set the hard resource limits. If the -S option is used as well, ulimit will set both the hard and the soft resource limits. Otherwise, ulimit will set just the soft resource limits. The behaviours when neither command-line option is specified or both are do not match the behaviours of (some) shells. However, note that even shells do not agree with one another on what to do in those two cases. For script clarity, the recommended use is to explicitly use -H for hard only and -S for soft only in separate invocations of the command, and avoid -H -S combined in a single invocation. This not only prevents misunderstanding by shell script programmers, it also clarifies the order in which limits are being set. The following limit options are available: -a KiBsets RLIMIT_AS, RLIMIT_DATA, RLIMIT_MEMLOCK, and RLIMIT_STACK -c blockssets RLIMIT_CORE -d KiBsets RLIMIT_DATA -e numbersets RLIMIT_NICE (only on some operating systems) -f blockssets RLIMIT_FSIZE -i nsets RLIMIT_SIGPENDING (only on some operating systems) -l KiBsets RLIMIT_MEMLOCK -m KiBsets RLIMIT_RSS -n nsets RLIMIT_NOFILE -p countsets RLIMIT_PIPE (only on some operating systems) -q countsets RLIMIT_MSGQUEUE (only on some operating systems) -s KiBsets RLIMIT_STACK -t secondssets RLIMIT_CPU -u nsets RLIMIT_NPROC -v KiBsets RLIMIT_AS -x nsets RLIMIT_LOCKS (only on some operating systems) See setrlimit2 for an explanation of the effects of these limits and the privileges that are sometimes required. To set an "infinite" limit, use the text unlimited for the limit value. Similarly, the text = or hard will use the current value of the hard limit as the value. (This is particularly useful when setting soft limits, as it provides a simple means of setting the soft limit to the hard limit ceiling without knowing its current value.) Special treatment is given to the -a option because it sets multiple limits at once. An attempt to set any one soft limit greater than the matching hard limit will be silently converted into an attempt to set the soft limit equal to the hard limit. Some limits are set in units of kilobinarybytes and blocks. For commands with finer granularity, see softlimit1 and hardlimit1. Jonathan de Boyne Pollard