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After testing JailKeeper I decided that it is definitely NOT the best approach to sandboxing applications, as services have to access sensitive data before they're detected and killed. In addition, because of the way processes are handled on UNIX systems, processes are not necessarily killed immediately, and there is actually no way to guarantee that a process can be killed immediately. It could take upwards of a full second to kill a rogue script, during which the script could delete or rewrite, or just read important files.

I recommend carefully using chroot jails, or, like Cloud9, spinning up new virtual servers in the cloud to execute arbitrary code.

What JailKeeper can be useful for is analyzing scripts and flagging potentially-malicious users, but it should strictly be treated as a logging or monitoring tool, not a security option.

JailKeeper is not currently being used in any production environments to my knowledge, and it's likely to remain that way.

You have been warned!


JailKeeper was created for my needs on SpanDeX.io. SpanDeX and similar cloud services must run otherwise-unsecured shell scripts (in our case, LaTeX code which is turing-complete and can access the filesystem). Obviously this has huge security implications. Chroot jails make me a little uneasy and seem quite difficult to manage, and easy to break out of (though I'm open to decent, lightweight alternatives). SmartOS zones seem like a better choice but I don't understand them yet ;)

Thus, this is my first attempt at an alternative solution, which is to use truss or dtruss (Solaris/SmartOS or Mac OS X, respectively) to monitor all the input/output of a spawned child process. We can immediately see if a process attempts to open a file that it shouldn't, kill the process, and notify the user (and server admins) that something funny is going on.

Warning: I have only extensively tested this on Joyent's SmartMachines, and I believe that there's something wrong with dtruss on Mac OS 10.8 so I haven't been able to test extensively on my local machine. Thus SmartOS/Solaris is supported well, but YMMV with other operating systems.


You know the drill:

npm install jailkeeper


Create a new JailKeeper and then call JailKeeper.spawn, just as you would use child_process.spawn:

var jail = new JailKeeper();
var childProcess = jail.spawn('echo "hello world"', [], { cwd: './tmp/jail1' });
childProcess.stdout.on('data', function (data) {
  console.log('Should say hello world: ', data.toString());

JailKeeper attaches itself to that child process and ensures that only files within the child's initial CWD are read or written to.

You can allow a jailed process more rights:

var jail = new JailKeeper(childProcess, { read: ['/usr/bin'], write: ['./tmp/jail2'] });

This allows the jail to access binaries in /usr/bin and write to ./tmp/jail2.

JailKeeper is an EventEmitter so you can attach to this event:

jail.on('jailbreak', function (message) {
  // Super sad!
  console.log('User tried to jailbreak by attempting to "' + message.mode + '"  the file ' + message.file);
jail.on('exit', function (code) {

The JailKeeper itself dies upon jailbreak, or when the child process otherwise executes.


Please contact me with any security concerns or ideas to make this more awesome:





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