forkpty fails for jailed linux user

Question

I have a Ubuntu 12.04 setup on the server. Every registered user is also registered as linux user & jailed with limited system resource access through /etc/security/limits.conf .

I tried running a server as one of the registered users. The app is a nodejs app - http://github.com/pocha/terminal-codelearn . It uses https://github.com/chjj/pty.js to create a Pseudo Terminal for every user which comes to the nodejs app.

The app fails with 'forkpty(3) failed' error pointed to line 184 of https://github.com/chjj/pty.js/blob/65dd89fd8f87de914ff1814362918d7bd87c9cbf/src/unix/pty.cc

pid_t pid = pty_forkpty(&master, name, NULL, &winp);

if (pid) {
  for (i = 0; i < argl; i++) free(argv[i]);
  delete[] argv;
  for (i = 0; i < envc; i++) free(env[i]);
    delete[] env;
  free(cwd);
}

switch (pid) {
  case -1:
    return ThrowException(Exception::Error(
    String::New("forkpty(3) failed.")));

I am able to successfully deploy the app on http://nitrous.io . They probably have similar way to jail user. I tried running ulimits -a & matched every value except for pending signal. Somehow on my server, the maximum pending signal value does not exceed around 90k value while it is 584k on Nitrous server.

Below is the ulimit -a output from Nitrous server

ulimit -a

core file size          (blocks, -c) 0
data seg size           (kbytes, -d) unlimited
scheduling priority             (-e) 0
file size               (blocks, -f) unlimited
pending signals                 (-i) 548288
max locked memory       (kbytes, -l) 64
max memory size         (kbytes, -m) unlimited
open files                      (-n) 512
pipe size            (512 bytes, -p) 8
POSIX message queues     (bytes, -q) 819200
real-time priority              (-r) 0
stack size              (kbytes, -s) 8192
cpu time               (seconds, -t) unlimited
max user processes              (-u) 256
virtual memory          (kbytes, -v) unlimited
file locks                      (-x) unlimited

The app fails on heroku with exact similar error.

Can anybody help on how to make the app run on my server the way it works on nitrous.io

Answer 1

I am not sure if I understand POSIX type. But I figured out that in my jailed environment there was no /dev/ptmx & /dev/pts/* . I googled & created them & it started working.

Answer 2

I know that heroku fails to forkpty because they're not actually running POSIX, just very posix-like. So some things, like forkpty, just don't work. I don't think there's a way around that :( wish there were.