node-posix

The missing POSIX system calls for Node.

FAQ

• Q: Why?
• A: Because the Node core has a limited set of POSIX system calls.
• Q: How mature/stable is this?
• A: Each version released in NPM has decent automated test coverage. The module has been successfully used in busy production sites for several years.
• Q: I have a feature request/bug report...
• A: Please submit a pull request or an issue ticket at https://github.com/ohmu/node-posix

Compatibility and API Stability

• Some degree of POSIX compliance is sought after, but this module is not always restricted by the standard. For example posix.openlog() also supports non-POSIX facility codes.
• node-posix version format: MAJOR.MINOR.PATCH
• PATCH version upgrades will not break backward compatibility, so it should be safe to upgrade from 1.0.0 to 1.0.1, 1.0.2, etc.
• MAJOR and MINOR version upgrades probably break backward-compatibility in some way, which may or may not affect your module.
• Recommended way to define a version dependency to node-posix in your package.json: "dependencies": { "posix": "1.0.x" }
• Update the version in package.json manually after validating compatibility with new node-posix MAJOR and MINOR releases).
• "package.json dependencies done right": http://blog.nodejitsu.com/package-dependencies-done-right

Related modules

Other extension modules that provide POSIX/Unix/Linux/BSD functionality:

• glob() http://npm.im/glob
• getrusage() http://npm.im/getrusage
• chroot(), daemonization http://npm.im/daemon-tools
• iconv() http://npm.im/iconv
• mmap() http://npm.im/mmap
• PAM authentication, flock() and mkstemp() http://npm.im/unixlib
• execvp() http://npm.im/kexec

General Information

User and Group ID Management

• posix.getgid() is an alias to Node core process.getgid()
• posix.getuid() is an alias to Node core process.getuid()
• posix.setgid() is an alias to Node core process.setgid()
• posix.setuid() is an alias to Node core process.setuid(), NOTE: should be used carefully due to inconsistent behavior under different operating systems, see http://www.cs.ucdavis.edu/~hchen/paper/usenix02.html

Resource limits

• ulimit() is obsolete, use posix.setrlimit() instead.

General usage

• Installation: npm install posix
• In your code: var posix = require('posix');

POSIX System Calls

posix.chroot(path)

Changes the root directory of the calling process to that specified in path. This directory will be used for pathnames beginning with /. The root directory is inherited by all children of the calling process.

The working directory is also automatically set to the new root directory.

NOTE: Please be aware of the limitations of chroot jails:

• "Best Practices for UNIX chroot() Operations": http://www.unixwiz.net/techtips/chroot-practices.html
• "How to break out of a chroot() jail": http://www.bpfh.net/simes/computing/chroot-break.html

Example:

posix.chroot('/somewhere/safe');

posix.getegid()

Returns the current process's effective group ID.

console.log('Effective GID: ' + posix.getegid());

posix.geteuid()

Returns the current process's effective user ID.

console.log('Effective UID: ' + posix.geteuid());

posix.getgrnam(group)

Get the group database entry for the given group. group can be specified either as a numeric GID or a group name (string).

var util = require('util');
util.inspect(posix.getgrnam('wheel'));

Example output of above:

{ name: 'wheel', passwd: '*', gid: 0, members: [ 'root' ] }

posix.getpgid(pid)

Return the process group ID of the current process (posix.getpgid(0)) or of a process of a given PID (posix.getpgid(PID)).

console.log('My PGID: ' + posix.getpgid(0));
console.log('init's PGID: ' + posix.getpgid(1));

posix.setpgid(pid)

Return the process group ID of the current process (posix.setpgid(0, PGID)) or of a process of a given PID (posix.getpgid(PID, PGID)).

// move process into it's own process group
posix.setpgid(process.pid, process.pid)

posix.getppid()

Returns the parent process's PID.

console.log('Parent PID: ' + posix.getppid());

posix.getpwnam(user)

Get the user database entry for the given user. user can be specified either as a numeric UID or a username (string).

var util = require('util');
util.inspect(posix.getpwnam('root'));

Example output of above:

{ name: 'root',
  passwd: '*',
  uid: 0,
  gid: 0,
  gecos: 'System Administrator',
  shell: '/bin/sh',
  dir: '/var/root' }

posix.getrlimit(resource)

Get resource limits. (See getrlimit(2).)

The soft limit is the value that the kernel enforces for the corresponding resource. The hard limit acts as a ceiling for the soft limit: an unprivileged process may only set its soft limit to a value in the range from 0 up to the hard limit, and (irreversibly) lower its hard limit.

A limit value of null indicates "unlimited" (RLIM_INFINITY).

Supported resources:

'core' (RLIMIT_CORE) Maximum size of core file. When 0 no core dump files are created.

'cpu' (RLIMIT_CPU) CPU time limit in seconds. When the process reaches the soft limit, it is sent a SIGXCPU signal. The default action for this signal is to terminate the process.

'data' (RLIMIT_DATA) The maximum size of the process's data segment (initialized data, uninitialized data, and heap).

'fsize' (RLIMIT_FSIZE) The maximum size of files that the process may create. Attempts to extend a file beyond this limit result in delivery of a SIGXFSZ signal.

'nofile' (RLIMIT_NOFILE) Specifies a value one greater than the maximum file descriptor number that can be opened by this process.

'nproc' (RLIMIT_NPROC) The maximum number of processes (or, more precisely on Linux, threads) that can be created by this process. (Note: Only Linux, OS X, and BSDs support the 'nproc' resource limit. An error will be raised on unsupported platforms.)

'stack' (RLIMIT_STACK) The maximum size of the process stack, in bytes. Upon reaching this limit, a SIGSEGV signal is generated.

'as' (RLIMIT_AS) The maximum size of the process's virtual memory (address space) in bytes.

var limits = posix.getrlimit('nofile');
console.log('Current limits: soft=' + limits.soft + ', max=' + limits.hard);

posix.initgroups(user, group)

Sets the group access list to all groups of which user is a member. The additional group group is also added to the list.

posix.initgroups("node", "httpd");  // all groups of 'node' plus 'httpd'

posix.setegid(gid)

Sets the Effective group ID of the current process. gid can be either a numeric GID or a group name (string).

posix.setegid(0); // set effective group UID to "wheel"
posix.setegid('nobody');

posix.seteuid(uid)

Sets the Effective user ID of the current process. uid can be either a numeric UID or a username (string).

posix.seteuid(0); // set effective UID to "root"
posix.seteuid('nobody');

posix.setregid(rgid, egid)

Sets the Real and Effective group IDs of the current process. rgid and egid can be either a numeric UIDs or group names (strings). A value of -1 means that the corresponding GID is left unchanged.

posix.setregid(-1, 1000); // just set the EGID to 1000
posix.setregid('www-data', 'www-data'); // change both RGID and EGID to "www-data"

posix.setreuid(ruid, euid)

Sets the Real and Effective user IDs of the current process. ruid and euid can be either a numeric UIDs or usernames (strings). A value of -1 means that the corresponding UID is left unchanged.

IMPORTANT NOTE: what happens to the Saved UID when setreuid() is called is operating system dependent. For example on OSX the Saved UID seems to be set to the previous EUID. This means that the process can escape back to EUID=0 simply by calling setreuid(0, 0). A workaround for this is to call posix.setreuid(ruid, euid) twice with the same arguments.

posix.setreuid(-1, 1000); // just set the EUID to 1000
posix.setreuid('nobody', 'nobody'); // change both RUID and EUID to "nobody"

posix.setrlimit(resource, limits)

Set resource limits. (See setrlimit(2).) Supported resource types are listed under posix.getrlimit.

The limits argument is an object in the form { soft: SOFT_LIMIT, hard: HARD_LIMIT }. Current limit values are used if either soft or hard key is not specifing in the limits object. A limit value of null indicates "unlimited" (RLIM_INFINITY).

// raise maximum number of open file descriptors to 10k, hard limit is left unchanged
posix.setrlimit('nofile', { soft: 10000 });

// enable core dumps of unlimited size
posix.setrlimit('core', { soft: null, hard: null });

posix.setsid()

Creates a session and sets the process group ID. Returns the process group ID.

console.log('Session ID: ' + posix.setsid());

Syslog

posix.openlog(identity, options, facility)

Open a connection to the logger.

Arguments:

• identity - defines the name of the process visible in the logged entries.
• options - set of option flags (see below).
• facility - facility code for the logged messages (see below).

Options:

• 'cons' - Log to the system console on error.
• 'ndelay' - Connect to syslog daemon immediately.
• 'nowait' - Do not wait for child processes.
• 'odelay' - Delay open until syslog() is called.
• 'pid' - Log the process ID with each message.

Facilities:

NOTE: only 'user' and 'local0' .. 'local7' are defined in the POSIX standard. However, the other codes should be pretty well supported on most platforms.

• 'kern'
• 'user'
• 'mail'
• 'news'
• 'uucp'
• 'daemon'
• 'auth'
• 'cron'
• 'lpr'
• 'local0' .. 'local7'

Example:

posix.openlog('myprog', {odelay: true, pid: true}, 'local7');

posix.closelog()

Close connection to the logger.

posix.setlogmask(mask)

Sets a priority mask for log messages. Further posix.syslog() messages are only sent out if their priority is included in the mask. Priorities are listed under posix.syslog().

// only send the most critical messages
posix.setlogmask({emerg:true, alert: true, crit: true});

posix.syslog(priority, message)

Send a message to the syslog logger using the given priority.

Priorities:

• 'emerg'
• 'alert'
• 'crit'
• 'err'
• 'warning'
• 'notice'
• 'info'
• 'debug'

Example:

posix.syslog('info', 'hello, world!');

hostname

posix.gethostname()

Returns the hostname of the operating system.

posix.sethostname(hostname)

Sets the hostname of the operating system.

Example:

posix.sethostname('beefheart');

swap

posix.swapon(path, swapflags)

Enable the swap device located at path. swapflags is an optional array of strings to define the flags of the swap device, being available prefer and discard.

posix.swapoff(path)

Disable the swap device located at path.

Credits

• Some of the documentation strings stolen from Linux man pages.
• posix.seteuid etc. implementation is based on Node core project SetUid
• Thank you for your contributions: Igor Pashev, Dan Bornstein, Jamie Paton, Nick Muerdter, Oskari Saarenmaa, Theo Schlossnagle, Alex Potsides, Robey Pointer, Stephen Sugden, Dave Longley, Jesús Leganés-Combarro

LICENSE

Copyright (c) 2011-2015 Mika Eloranta

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.