unix: Support for UNIX-like systems

Table of content


The unix: module provides access to features that only make sense on UNIX-like operating systems, such as Linux, FreeBSD, and macOS.

On non-UNIX operating systems, such as MS Windows, this namespace does not exist and use unix will fail. Use the $platform:is-unix variable to determine if this namespace is usable.



A map describing resource limits of the current process.

Each key is a string corresponds to a resource, and each value is a map with keys &cur and &max, describing the soft and hard limits of that resource. A missing &cur key means that there is no soft limit; a missing &max key means that there is no hard limit.

The following resources are supported, some only present on certain OSes:

  • core: size of a core file, in bytes.

  • cpu: CPU time, in seconds.

  • data: size of the data segment, in bytes

  • fsize: size of a file created by the process, in bytes.

  • memlock: size of locked memory, in bytes.

  • nofile: number of file descriptors.

  • nproc: number of processes for the user.

  • rss: resident set size, in bytes.

  • stack: size of the stack segment, in bytes.

  • as: size of the address space, in bytes. Available on Linux, FreeBSD and NetBSD.

  • nthr: number of threads for the user. NetNSD only.

  • sbsize: size of socket buffers, in bytes. NetBSD only.

  • locks: number of file locks. Linux only.

  • msgqueue: size of message queues, in bytes. Linux only.

  • nice: ceiling of 20 - nice value. Linux only.

  • rtprio: real time priority. Linux only.

  • rttime: real-time CPU time, in seconds. Linux only.

  • sigpending: number of signals queued. Linux only.

For the exact semantics of each resource, see the man page of getrlimit: Linux, macOS, FreeBSD, NetBSD, OpenBSD. A key foo in the Elvish API corresponds to RLIMIT_FOO in the C API.


~> put $unix:rlimits
▶ [&nofile=[&cur=(num 256)] &fsize=[&] &nproc=[&max=(num 2666) &cur=(num 2666)] &memlock=[&] &cpu=[&] &core=[&cur=(num 0)] &stack=[&max=(num 67092480) &cur=(num 8372224)] &rss=[&] &data=[&]]
~> # mimic Bash's "ulimit -a"
~> keys $unix:rlimits | order | each {|key|
     var m = $unix:rlimits[$key]
     fn get {|k| if (has-key $m $k) { put $m[$k] } else { put unlimited } }
     printf "%-7v %-9v %-9v\n" $key (get cur) (get max)
core    0         unlimited
cpu     unlimited unlimited
data    unlimited unlimited
fsize   unlimited unlimited
memlock unlimited unlimited
nofile  256       unlimited
nproc   2666      2666
rss     unlimited unlimited
stack   8372224   67092480
~> # Decrease the soft limit on file descriptors
~> set unix:rlimits[nofile][cur] = 100
~> put $unix:rlimits[nofile]
▶ [&cur=(num 100)]
~> # Remove the soft limit on file descriptors
~> del unix:rlimits[nofile][cur]
~> put $unix:rlimits[nofile]
▶ [&]


The file mode creation mask. Its value is a string in Elvish octal representation; e.g. 0o027. This makes it possible to use it in any context that expects a $number.

When assigning a new value a string is implicitly treated as an octal number. If that fails the usual rules for interpreting numbers are used. The following are equivalent: set unix:umask = 027 and set unix:umask = 0o27. You can also assign to it a float64 data type that has no fractional component. The assigned value must be within the range [0 … 0o777], otherwise the assignment will throw an exception.

You can do a temporary assignment to affect a single command; e.g. { tmp umask = 077; touch a_file }. After the command completes the old umask will be restored. Warning: Since the umask applies to the entire process, not individual threads, changing it temporarily in this manner is dangerous if you are doing anything in parallel, such as via the peach command.