Fix ^C ignored issue on CentOS 6.8.

[russjones]

Purpose

On certain operating systems (like CentOS 6.8) when sysvinit launches Teleport it configures it to ignore SIGINT. You can see this behavior by connecting to a Teleport node started by sysvinit typing the following:

$ nc -l localhost 12345
^C^C^C^C

If you strace the process and manually send SIGINT you'll see it receives SIGINT but does nothing:

$ strace -p 32867
Process 32867 attached
accept(3, 0x7ffc24beb650, [128])        = ? ERESTARTSYS (To be restarted if SA_RESTART is set)
--- SIGINT {si_signo=SIGINT, si_code=SI_USER, si_pid=33049, si_uid=0} ---
accept(3,

To resolve this issue, we need to reset the signal handler to the default signal handler so SIGINT can be processed.

Implementation

Since Go does not allow us to directly reset the signal handler, we have to use cgo to call the following code when a Teleport process starts:

#include <signal.h>
signal(SIGINT, SIG_DFL)

Related Issues

Fixes #981

References

• http://garethrees.org/2015/08/07/ping/
• openssh/openssh-portable@4e0f5e1