Reference

# Module `lposix`

## Functions

abort () | Abort the program immediately.
raise (nsig) | Raise a signal on this process.
isgraph (character) | Check for any printable character except space.
isprint (character) | Check for any printable character including space.
errno (n) | Describe an error code/and or read errno
set_errno (n) | Set errno.
realpath (path) | Find canonicalized absolute pathname.
basename (path) | File part of path.
dirname (path) | Directory name of path.
dir (path) | Contents of directory.
fnmatch (pat, name, flags) | Match a filename against a shell pattern.
glob (pat) | Find all files in this directory matching a shell pattern.
files (path) | Iterator over all files in this directory.
getcwd () | Current working directory for this process.
mkdir (path) | Make a directory.
chdir (path) | Set the working directory.
rmdir (path) | Remove a directory.
unlink (path) | Unlink a file.
link (target, link, soft) | Create a link.
readlink (path) | Read value of a symbolic link.
access (path, mode) | Check real user's permissions for a file.
fileno (file) | File descriptor corresponding to a Lua file object.
mkfifo (path) | Make a FIFO pipe.
mkstemp (templ) | Create a unique temporary file.
mkdtemp (templ) | Create a unique temporary directory.
exec (path, ..., t) | Execute a program without using the shell.
execp (path, ..., t) | Execute a program using the shell.
fork () | Fork this program.
_exit (return) | Terminate the calling process.
rpoll (file, timeout) | Wait for some event on a file descriptor.
poll (list, timeout) | Wait for events on multiple file descriptors.
wait (pid) | Wait for the given process.
kill (pid, sig) | Send a signal to the given process.
killpg (pgrp, sig) | Send a signal to the given process group.
setpid (what, id, gid) | Set the uid, euid, gid, egid, sid or pid & gid.
sleep (seconds) | Sleep for a number of seconds.
nanosleep (seconds, nanoseconds) | Sleep with nanosecond precision.
msgget (key, flags, mode) | Get a message queue identifier
msgsnd (id, type, message, flags) | Send message to a message queue
msgrcv (id, size, type, flags) | Receive message from a message queue
setenv (name, value, over) | Set an environment variable for this process.
getenv (name) | Get value of environment variable, or all variables.
umask (mode) | Set file mode creation mask.
openpt (oflags) | Open a pseudoterminal.
grantpt (file) | Grant access to a slave pseudoterminal
unlockpt (file) | Unlock a pseudoterminal master/slave pair
ptsname (file) | Get the name of a slave pseudo-terminal
open (path, oflags, mode) | Open a file.
close (fd) | Close an open file descriptor.
dup (fd) | Duplicate an open file descriptor.
dup2 (oldfd, newfd) | Duplicate one open file descriptor to another, closing the new one if necessary.
pipe () | Creates a pipe.
chmod (path, mode) | Change the mode of the path.
read (fd, count) | Read bytes from a file.
write (fd, buf) | Write bytes to a file.
chown (path, uid, gid) | Change ownership of a file.
utime (path, mtime, atime) | Change file last access and modification times.
getpid (...) | Get process identifiers.
hostid () | Get host id.
ttyname (fd) | Name of a terminal device.
ctermid () | Name of controlling terminal.
getpasswd (user, ...) | Get the password entry for a user.
getgroup (group) | Information about a group.
getgroups () | Get list of supplementary group IDs.
times (...) | Get the current process times.
stat (path, ...) | Information about an existing file path.
statvfs (path, ...) | Get file system statistics.
fcntl (fd, cmd, arg) | Manipulate file descriptor.
isatty (fd) | Test whether a file descriptor refers to a terminal.
uname (optional) | Return information about this machine.
pathconf (path, ...) | Get a value for a configuration option for a filename.
sysconf (...) | Get configuration information at runtime.
openlog (ident, option, facility) | Open the system logger.
syslog (priority, message) | Write to the system logger.
closelog () | Close system log.
setlogmask (bitwise) | Set log priority mask.
crypt (string, salt) | Encrypt a password.
setrlimit (resource, softlimit, hardlimit) | Set a resource limit for subsequent child processes.
getrlimit (resource) | Get resource limits for this process.

## Time and date

gettimeofday () | Get time of day.
time () | Get current time.
localtime (t) | Convert time in seconds to table.
gmtime (t) | Convert UTC time in seconds to table.
clock_getres (name) | Find the precision of a clock.
clock_gettime (name) | Read a clock.
strftime (tm) | Write a time out according to a format.
mktime (tm) | Convert a time table into a time value.
getopt (arg, shortopts, longopts) | Parse command-line options.
signal (signum, handler, flags) | Install a signal handler for this signal number.
sync () | commit buffer cache to disk
fsync (fd) | synchronize a file's in-core state with storage device
fdatasync (fd) | synchronize a file's in-core state with storage device without metadata
lseek (fd, offset, whence) | reposition read/write file offset
nice (inc) | change process priority

## Functions

abort ()
  Abort the program immediately.

  ### see also:

  abort(3)
raise (nsig)
  Raise a signal on this process.

  ### Parameters:

  - nsig int

  ### Returns:

  integer error code

  ### see also:

  raise(3)
isgraph (character)
  Check for any printable character except space.

  ### Parameters:

  - character string to check

  ### Returns:

  true if character is in the class

  ### see also:

  isprint(3)
isprint (character)
  Check for any printable character including space.

  ### Parameters:

  - character string to check

  ### Returns:

  true if character is in the class

  ### see also:

  isgraph(3)
errno (n)
  Describe an error code/and or read errno

  ### Parameters:

  - n int optional error code (default: current value of errno )

  ### Returns:

  1. description
  2. error code

  ### see also:

  errno(3)
set_errno (n)
  Set errno.

  ### Parameters:

  - n int error code

  ### see also:

  errno(3)
realpath (path)
  Find canonicalized absolute pathname.

  ### Parameters:

  - path string

  ### Returns:

  1. canonicalized absolute path, or nil on error
  2. error message if failed

  ### see also:

  realpath(3)
basename (path)
  File part of path.

  ### Parameters:

  - path string

  ### Returns:

  file part

  ### see also:

  basename(3)
dirname (path)
  Directory name of path.

  ### Parameters:

  - path string

  ### Returns:

  directory part

  ### see also:

  dirname(3)
dir (path)
  Contents of directory.

  ### Parameters:

  - path string optional (default .)

  ### Returns:

  contents as table

  ### see also:

  dir.lua
fnmatch (pat, name, flags)
  Match a filename against a shell pattern.

  ### Parameters:

  - pat string shell pattern
  - name string filename
  - flags int optional (default 0)

  ### Returns:

  true or false

  ### Raises:

  error if fnmatch failed

  ### see also:

  fnmatch(3)
glob (pat)
  Find all files in this directory matching a shell pattern.

  ### Parameters:

  - pat string shell pattern

  ### Returns:

  table of matching filenames

  ### see also:

  - glob(3)
  - glob.lua
files (path)
  Iterator over all files in this directory.

  ### Parameters:

  - path string optional (default .)

  ### Returns:

  an iterator
getcwd ()
  Current working directory for this process.

  ### Returns:

  path

  ### see also:

  getcwd(3)
mkdir (path)
  Make a directory.

  ### Parameters:

  - path string

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  mkdir(2)
chdir (path)
  Set the working directory.

  ### Parameters:

  - path string

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  chdir(2)

  ### Usage:

      status, errstr, errno = posix.chdir("/var/tmp")

rmdir (path)
  Remove a directory.

  ### Parameters:

  - path string

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  rmdir(2)
unlink (path)
  Unlink a file.

  ### Parameters:

  - path string

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  unlink(2)
link (target, link, soft)
  Create a link.

  ### Parameters:

  - target string name
  - link string name
  - soft bool link

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  - link(2)
  - symlink(2)
readlink (path)
  Read value of a symbolic link.

  ### Parameters:

  - path string

  ### Returns:

  1. link target on success, error otherwise
  2. error message if failed

  ### see also:

  readlink(2)
access (path, mode)
  Check real user's permissions for a file.

  ### Parameters:

  - path string
  - mode string optional, can contain 'r','w','x' and 'f' (default 'f')

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  access(2)

  ### Usage:

      status, errstr, errno = posix.access("/etc/passwd", "rw")

fileno (file)
  File descriptor corresponding to a Lua file object.

  ### Parameters:

  - file Lua file object

  ### Returns:

  1. handle on success, nil otherwise
  2. error message if failed.
mkfifo (path)
  Make a FIFO pipe.

  ### Parameters:

  - path string

  ### Returns:

  1. handle on success, nil otherwise
  2. error message if failed.

  ### see also:

  mkfifo(2)
mkstemp (templ)
  Create a unique temporary file.

  ### Parameters:

  - templ string pattern that ends in "XXXXXX"

  ### Returns:

  1. file descriptor, nil otherwise
  2. name on success, error otherwise

  ### see also:

  mkstemp(3)

  ### Usage:

      posix.mkstemp 'wooXXXXXX'

mkdtemp (templ)
  Create a unique temporary directory.

  ### Parameters:

  - templ string pattern that ends in six 'X' characters

  ### Returns:

  1. path on success, nil otherwise
  2. error message if failed

  ### see also:

  mkdtemp(3)
exec (path, ..., t)
  Execute a program without using the shell.

  ### Parameters:

  - path string
  - ... any arguments, or
  - t table of arguments (can include index 0)

  ### Returns:

  1. return code, nil otherwise
  2. error message if failed.

  ### see also:

  execve(2)
execp (path, ..., t)
  Execute a program using the shell.

  ### Parameters:

  - path string
  - ... any arguments, or
  - t table of arguments (can include index 0)

  ### Returns:

  1. return code, nil otherwise
  2. error message if failed.

  ### see also:

  execve(2)
fork ()
  Fork this program.

  ### Returns:

  1. return code, nil otherwise
  2. error message if failed.

  ### see also:

  - fork(2)
  - fork.lua
  - fork2.lua
_exit (return)
  Terminate the calling process.

  ### Parameters:

  - return int status

  ### see also:

  _exit(2)
rpoll (file, timeout)
  Wait for some event on a file descriptor. Adapted from http://lua-users.org/lists/lua-l/2007-11/msg00346.html

  ### Parameters:

  - file int descriptor
  - timeout int

  ### Returns:

  1. return code, nil otherwise
  2. error message if failed.

  ### see also:

  poll(2)
poll (list, timeout)
  Wait for events on multiple file descriptors.

  ### Parameters:

  - list of file descriptors
  - timeout int optional (default -1)

  ### Returns:

  1. return code, nil otherwise
  2. error message if failed.

  ### see also:

  - poll(2)
  - poll.lua
wait (pid)
  Wait for the given process.

  ### Parameters:

  - pid int optional (default -1 (any child process))

  ### Returns:

  1. pid of terminated child, nil on error
  2. how child ended ("exited", "killed" or "stopped"), or error message on error.
  3. status value (computed with WEXITSTATUS, WTERMSIG or WSTOPSIG as appropriate), or nothing on error.

  ### see also:

  waitpid(2)
kill (pid, sig)
  Send a signal to the given process.

  ### Parameters:

  - pid int process id
  - sig int optional (default SIGTERM)

  ### Returns:

  1. return code, nil otherwise
  2. error message if failed.

  ### see also:

  kill(2)
killpg (pgrp, sig)
  Send a signal to the given process group.

  ### Parameters:

  - pgrp int group id
  - sig int optional (default SIGTERM)

  ### Returns:

  1. return code, nil otherwise
  2. error message if failed.

  ### see also:

  killpg(2)
setpid (what, id, gid)
  Set the uid, euid, gid, egid, sid or pid & gid.

  ### Parameters:

  - what string one of 'u', 'U', 'g', 'G', 's', 'p' (upper-case means "effective")
  - id (uid, gid or pid for every value of `what` except 's')
  - gid (only for `what` value 'p')

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed

  ### see also:

  - setuid(2)
  - seteuid(2)
  - setgid(2)
  - setegid(2)
  - setsid(2)
  - setpgid(2)
sleep (seconds)
  Sleep for a number of seconds.

  ### Parameters:

  - seconds int

  ### Returns:

  code

  ### see also:

  sleep(3)
nanosleep (seconds, nanoseconds)
  Sleep with nanosecond precision.

  ### Parameters:

  - seconds int
  - nanoseconds int

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed, or the remaining time as two results `tv_sec`, `tv_nsec` if return value is `EINTR`.

  ### see also:

  nanosleep(2)
msgget (key, flags, mode)
  Get a message queue identifier

  ### Parameters:

  - key int
  - flags int (optional, default - 0)
  - mode int (optional, default - 0777)

  ### Returns:

  1. message queue identifier on success
  2. nil and error message if failed

  ### see also:

  msgget(2)
msgsnd (id, type, message, flags)
  Send message to a message queue

  ### Parameters:

  - id int
    - message queue identifier returned by msgget
  - type int
    - message type
  - message string
  - flags int (optional, default - 0)

  ### Returns:

  1. 0 on success
  2. nil and error message if failed

  ### see also:

  msgsnd(2)
msgrcv (id, size, type, flags)
  Receive message from a message queue

  ### Parameters:

  - id int
    - message queue identifier returned by msgget
  - size int
    - maximum message size
  - type int
    - message type (optional, default - 0)
  - flags int (optional, default - 0)

  ### Returns:

  1. message type and message text on success
  2. nil, nil and error message if failed

  ### see also:

  msgrcv(2)
setenv (name, value, over)
  Set an environment variable for this process. (Child processes will inherit this)

  ### Parameters:

  - name string
  - value string (maybe nil, meaning 'unset')
  - over non-nil prevents overwriting a variable

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  setenv(3)
getenv (name)
  Get value of environment variable, or all variables.

  ### Parameters:

  - name string if nil, get all

  ### Returns:

  value if name given, otherwise a name-indexed table of values.

  ### see also:

  getenv(3)

  ### Usage:

      for a,b in pairs(posix.getenv()) do print(a, b) end

umask (mode)
  Set file mode creation mask.

  ### Parameters:

  - mode string optional file creation mask string (default current mask; see chmod for format)

  ### Returns:

  previous umask

  ### see also:

  - umask(2)
  - chmod
openpt (oflags)
  Open a pseudoterminal.

  ### Parameters:

  - oflags int bitwise OR of the values `O_RDWR`, and possibly `O_NOCTTY` (all in the library's namespace)

  ### Returns:

  1. file descriptor on success, nil otherwise
  2. error message if failed.

  ### see also:

  - posix_openpt(3)
  - grantpt
  - ptsname
  - unlockpt
grantpt (file)
  Grant access to a slave pseudoterminal

  ### Parameters:

  - file descriptor returned by opening /dev/ptmx

  ### Returns:

  1. 0 on success
  2. nil, error message if failed.

  ### see also:

  - openpt
  - ptsname
  - unlockpt
unlockpt (file)
  Unlock a pseudoterminal master/slave pair

  ### Parameters:

  - file descriptor returned by opening /dev/ptmx

  ### Returns:

  1. 0 on success
  2. nil, error message if failed.

  ### see also:

  - openpt
  - ptsname
  - grantpt
ptsname (file)
  Get the name of a slave pseudo-terminal

  ### Parameters:

  - file descriptor returned by opening /dev/ptmx

  ### Returns:

  1. path name of the slave terminal device
  2. nil, error message if failed.

  ### see also:

  - openpt
  - grantpt
  - unlockpt
open (path, oflags, mode)
  Open a file.

  ### Parameters:

  - path string
  - oflags int bitwise OR of the values `O_RDONLY`, `O_WRONLY`, `O_RDWR`, `O_APPEND`, `O_CREAT`, `O_DSYNC`, `O_EXCL`, `O_NOCTTY`, `O_NONBLOCK`, `O_RSYNC`, `O_SYNC`, `O_TRUNC` (all in the library's namespace)
  - mode string (used with `O_CREAT`; see chmod for format)

  ### Returns:

  1. file descriptor on success, nil otherwise
  2. error message if failed.

  ### see also:

  - open(2)
  - chmod
close (fd)
  Close an open file descriptor.

  ### Parameters:

  - fd int

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  close(2)
dup (fd)
  Duplicate an open file descriptor.

  ### Parameters:

  - fd int

  ### Returns:

  1. file descriptor on success, nil otherwise
  2. error message if failed.

  ### see also:

  dup(2)
dup2 (oldfd, newfd)
  Duplicate one open file descriptor to another, closing the new one if necessary.

  ### Parameters:

  - oldfd int
  - newfd int

  ### Returns:

  1. new file descriptor on success, nil otherwise
  2. error message if failed.

  ### see also:

  dup2(2)
pipe ()
  Creates a pipe.

  ### Returns:

  1. fd read end
  2. fd write end

  ### see also:

  - pipe(2)
  - fork.lua
chmod (path, mode)

  Change the mode of the path. Modes are specified in one of the following formats:

  - "rwxrwxrwx" (e.g. "rw-rw-w--")
  - "ugoa+-=rwx" (e.g. "u+w")
  - "+-=rwx" (e.g. "+w")

  ### Parameters:

  - path string existing file path
  - mode string

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  chmod(2)

  ### Usage:

      posix.chmod('bin/dof','+x')

read (fd, count)
  Read bytes from a file.

  ### Parameters:

  - fd int the file descriptor
  - count int number of bytes to read

  ### Returns:

  1. string with at most `count` bytes, or nil on error
  2. error message if failed

  ### see also:

  read(2)
write (fd, buf)
  Write bytes to a file.

  ### Parameters:

  - fd int the file descriptor
  - buf string containing bytes

  ### Returns:

  1. number of bytes written on success, nil otherwise
  2. error message if failed.

  ### see also:

  write(2)
chown (path, uid, gid)
  Change ownership of a file.

  ### Parameters:

  - path string existing file path
  - uid (string or number)
  - gid (string or number)

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  chown(2)

  ### Usage:

      print(posix.chown("/etc/passwd",100,200)) -- will fail for a normal user, and hence print an error

utime (path, mtime, atime)
  Change file last access and modification times.

  ### Parameters:

  - path string existing file path
  - mtime int optional modification time (default current time)
  - atime int optional access time (default current time)

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  utime(2)
getpid (...)
  Get process identifiers.

  ### Parameters:

  - ... string types, each one of "egid", "euid", "gid", "uid", "pgrp", "pid", "ppid"

  ### Returns:

  ... values, or table of all ids if no option given

  ### Usage:

      posix.getpid 'pid' -- PID of current process

hostid ()
  Get host id.

  ### Returns:

  host id

  ### see also:

  gethostid(3)
ttyname (fd)
  Name of a terminal device.

  ### Parameters:

  - fd int optional file descriptor (default 0)

  ### Returns:

  string name

  ### see also:

  ttyname(3)
ctermid ()
  Name of controlling terminal.

  ### Returns:

  code

  ### see also:

  ctermid(3)
getpasswd (user, ...)
  Get the password entry for a user.

  ### Parameters:

  - user (name or id)
  - ... string field names, each one of "uid", "name", "gid", "passwd", "dir", "shell"

  ### Returns:

  ... values, or table of all fields if no option given

  ### Usage:

  -     for a,b in pairs(posix.getpasswd("root")) do print(a,b) end

  -     print(posix.getpasswd("root", "shell"))

getgroup (group)
  Information about a group.

  ### Parameters:

  - group id or name

  ### Returns:

  table `{name=name,gid=gid,0=member0,1=member1,...}`
getgroups ()
  Get list of supplementary group IDs.

  ### Returns:

  table of group IDs.

  ### see also:

  getgroups(2)
times (...)
  Get the current process times.

  ### Parameters:

  - ... string field names, each one of "utime", "stime", "cutime", "cstime", "elapsed"

  ### Returns:

  ... times, or table of all times if no option given

  ### see also:

  times(2)
stat (path, ...)
  Information about an existing file path.

  ### Parameters:

  - path string file path
  - ... string field names, each one of "mode", "ino", "dev", "nlink", "uid", "gid", "size", "atime", "mtime", "ctime", "type"

  ### Returns:

  ... values, or table of all fields if no option given

  ### see also:

  stat(2)

  ### Usage:

      for a, b in pairs(posix.stat("/etc/")) do print(a, b) end

statvfs (path, ...)
  Get file system statistics.

  ### Parameters:

  - path string any path within the mounted file system
  - ... string field names, each one of "bsize", "frsize", "blocks", "bfree", "bavail", "files", "ffree", "favail", "fsid", "flag", "namemax"

  ### Returns:

  ... values, or table of all fields if no option given

  ### see also:

  statvfs(3)
fcntl (fd, cmd, arg)
  Manipulate file descriptor.

  ### Parameters:

  - fd int file descriptor to act on
  - cmd int operation to perform
  - arg optional (default 0). Type and meaning of this param depends on `cmd`. Currently it expects arg to be a table for file lock related `cmd` and a number for all the rest. With file lock `cmd` the table should contain fields for flock structure (see example). When function returns the fields of the table get updated with corresponding values from flock structure (to comply with semantics of F_GETLK).

  ### Returns:

  1. integer return value depending on `cmd`, or nil on error
  2. error message if failed

  ### see also:

  - fcntl(2)
  - lock.lua
isatty (fd)
  Test whether a file descriptor refers to a terminal.

  ### Parameters:

  - fd int file descriptor to test

  ### Returns:

  1. 1 if fd is an open file descriptor referring to a terminal, or nil otherwise
  2. error message if failed

  ### see also:

  isatty(3)
uname (optional)
  Return information about this machine.

  ### Parameters:

  - optional string , contains zero or more of:
    - %m machine name
    - %n node name
    - %r release
    - %s sys name
    - %v version

    (default return all information available)

  ### Returns:

  1. information string on success, nil otherwise
  2. error message if failed

  ### see also:

  uname(2)
pathconf (path, ...)
  Get a value for a configuration option for a filename.

  ### Parameters:

  - path string optional (default ".")
  - ... string field names, each one of "LINKMAX", "MAXCANON", "NAMEMAX", "PIPEBUF", "CHOWNRESTRICTED", "NOTRUNC", "VDISABLE"

  ### Returns:

  ... values, or table of all fields if no option given

  ### see also:

  pathconf(3)

  ### Usage:

      for a, b in pairs(posix.pathconf("/dev/tty")) do print(a, b) end

sysconf (...)
  Get configuration information at runtime.

  ### Parameters:

  - ... string field names, each one of "ARGMAX", "CHILDMAX", "CLKTCK", "NGROUPSMAX", "STREAMMAX", "TZNAMEMAX", "OPENMAX", "JOBCONTROL", "VERSION"

  ### Returns:

  ... values, or table of all fields no option

  ### see also:

  sysconf(3)
openlog (ident, option, facility)
  Open the system logger.

  ### Parameters:

  - ident string all messages will start with this
  - option string optional, any combination of 'c' (directly to system console if an error sending), 'n' (no delay) or 'p' (show PID)
  - facility int optional (default LOG_USER)

  ### see also:

  syslog(3)
syslog (priority, message)
  Write to the system logger.

  ### Parameters:

  - priority int

    one of these values:

    - 1 Alert - immediate action
    - 2 Critcal
    - 3 Error
    - 4 Warning
    - 5 Notice
    - 6 Informational
  - message string

  ### see also:

  syslog(3)
closelog ()
  Close system log.

  ### see also:

  syslog(3)
setlogmask (bitwise)
  Set log priority mask.

  ### Parameters:

  - bitwise int OR of values from `LOG_EMERG`, `LOG_ALERT`, `LOG_CRIT`, `LOG_WARNING`, `LOG_NOTICE`, `LOG_INFO`, `LOG_DEBUG`

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.
crypt (string, salt)
  Encrypt a password. Not recommended for general encryption purposes.

  ### Parameters:

  - string string
  - salt string two-character string from [a-zA-Z0-9./]

  ### Returns:

  encrypted string

  ### see also:

  crypt(3)
setrlimit (resource, softlimit, hardlimit)
  Set a resource limit for subsequent child processes.

  ### Parameters:

  - resource string one of "core", "cpu", "data", "fsize", "nofile", "stack", "as"
  - softlimit optional (default keep current limit)
  - hardlimit optional (default keep current limit)

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  - getrlimit(2)
  - limit.lua

  ### Usage:

      posix.setrlimit("nofile", 1000, 2000)

getrlimit (resource)
  Get resource limits for this process.

  ### Parameters:

  - resource string one of "core", "cpu", "data", "fsize", "nofile", "stack", "as"

  ### Returns:

  1. softlimit, or nil if error
  2. hardlimit, or message on error

## Time and date

Time and date.

gettimeofday ()
  Get time of day.

  ### Returns:

  1. time in seconds
  2. remainder in nanoseconds

  ### see also:

  gettimeofday(2)
time ()
  Get current time.

  ### Returns:

  time in seconds since epoch
localtime (t)
  Convert time in seconds to table.

  ### Parameters:

  - t time in seconds since epoch (default now)

  ### Returns:

  time table: contains "is_dst","yearday","hour","min","year","month", "sec","weekday","monthday", "day" (the same as "monthday")
gmtime (t)
  Convert UTC time in seconds to table.

  ### Parameters:

  - t time in seconds since epoch (default now)

  ### Returns:

  time table as in localtime
clock_getres (name)
  Find the precision of a clock.

  ### Parameters:

  - name string of clock, one of "monotonic", "processcputimeid", or "threadcputimeid", or nil for realtime clock.

  ### Returns:

  1. seconds, or nil on error
  2. nanoseconds, or message on error
clock_gettime (name)
  Read a clock.

  ### Parameters:

  - name string of clock, one of "monotonic", "processcputimeid", or "threadcputimeid", or nil for realtime clock.

  ### Returns:

  1. seconds, or nil on error
  2. nanoseconds, or message on error
strftime (tm)
  Write a time out according to a format.

  ### Parameters:

  - tm optional time table (e.g from localtime ; default current time)

  ### see also:

  strftime(3)
mktime (tm)
  Convert a time table into a time value.

  ### Parameters:

  - tm time table as in localtime

  ### Returns:

  time in seconds since epoch
getopt (arg, shortopts, longopts)
  Parse command-line options.

  ### Parameters:

  - arg command line arguments
  - shortopts string e.g 'ho:v' (colon means 'receives argument')
  - longopts e.g. `{{'help','none',2},...}`

  ### see also:

  getopt.lua

  ### Usage:

      for ret, longindex, optind, optarg in posix.getopt (arg, shortopts[, longopts[, opterr[, optind]]]) do ... end

signal (signum, handler, flags)
  Install a signal handler for this signal number. N.B. Although this is the same API as signal(2), it uses sigaction for guaranteed semantics.

  ### Parameters:

  - signum int
  - handler function
  - flags optional the `sa_flags` element of `struct sigaction`

  ### Returns:

  previous handler function

  ### see also:

  - sigaction(2)
  - signal.lua
sync ()
  commit buffer cache to disk

  ### see also:

  sync(2)
fsync (fd)
  synchronize a file's in-core state with storage device

  ### Parameters:

  - fd int

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  fsync(2)
fdatasync (fd)
  synchronize a file's in-core state with storage device without metadata

  ### Parameters:

  - fd int

  ### Returns:

  1. 0 on success, nil otherwise
  2. error message if failed.

  ### see also:

  fdatasync(2)
lseek (fd, offset, whence)
  reposition read/write file offset

  ### Parameters:

  - fd int
  - offset int
  - whence int one of SEEKSET, SEEKCUR or SEEK_END

  ### Returns:

  1. new offset on success, nil otherwise
  2. error message if failed.

  ### see also:

  lseek(2)
nice (inc)
  change process priority

  ### Parameters:

  - inc int adds inc to the nice value for the calling process

  ### Returns:

  1. new nice value on success, nil otherwise
  2. error message if failed.

  ### see also:

  nice(2)

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