2015-07-30 02:03:55 +03:00
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/*
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* dumb-init is a simple wrapper program designed to run as PID 1 and pass
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* signals to its children.
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*
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* Usage:
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* ./dumb-init python -c 'while True: pass'
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*
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2015-10-02 23:31:35 +03:00
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* To get debug output on stderr, run with '-v'.
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2015-07-30 02:03:55 +03:00
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*/
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2015-09-05 01:19:17 +03:00
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#include <assert.h>
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2015-08-26 19:05:54 +03:00
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#include <errno.h>
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2015-10-02 23:31:35 +03:00
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#include <getopt.h>
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2015-07-30 02:03:55 +03:00
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#include <signal.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <unistd.h>
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2015-10-02 23:31:35 +03:00
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#include "VERSION.h"
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2015-07-30 02:03:55 +03:00
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2015-10-02 20:48:23 +03:00
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#define PRINTERR(...) do { \
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fprintf(stderr, "[dumb-init] " __VA_ARGS__); \
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} while (0)
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2015-08-26 19:05:54 +03:00
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#define DEBUG(...) do { \
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if (debug) { \
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2015-10-02 20:48:23 +03:00
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PRINTERR(__VA_ARGS__); \
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2015-08-26 19:05:54 +03:00
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} \
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} while (0)
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2015-09-05 01:19:17 +03:00
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pid_t child_pid = -1;
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2015-07-30 02:03:55 +03:00
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char debug = 0;
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2015-09-11 00:05:05 +03:00
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char use_setsid = 1;
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2015-07-30 02:03:55 +03:00
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2015-09-17 05:42:09 +03:00
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void forward_signal(int signum) {
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2015-09-05 01:19:17 +03:00
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if (child_pid > 0) {
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kill(use_setsid ? -child_pid : child_pid, signum);
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2015-10-02 20:48:23 +03:00
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DEBUG("Forwarded signal %d to children.\n", signum);
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2015-08-26 19:05:54 +03:00
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} else {
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2015-10-02 20:48:23 +03:00
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DEBUG("Didn't forward signal %d, no children exists yet.\n", signum);
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2015-08-10 19:32:56 +03:00
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}
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2015-07-30 02:03:55 +03:00
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}
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2015-09-19 07:59:31 +03:00
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/*
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* The dumb-init signal handler.
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*
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* The main job of this signal handler is to forward signals along to our child
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* process(es). In setsid mode, this means signaling the entire process group
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* rooted at our child. In non-setsid mode, this is just signaling the primary
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* child.
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*
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* In most cases, simply proxying the received signal is sufficient. If we
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* receive a job control signal, however, we should not only forward it, but
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* also sleep dumb-init itself.
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*
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* This allows users to run foreground processes using dumb-init and to
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* control them using normal shell job control features (e.g. Ctrl-Z to
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* generate a SIGTSTP and suspend the process).
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*
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* The libc manual is useful:
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* https://www.gnu.org/software/libc/manual/html_node/Job-Control-Signals.html
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*
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* When running in setsid mode, however, it is not sufficient to forward
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* SIGTSTP/SIGTTIN/SIGTTOU in most cases. If the process has not added a custom
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* signal handler for these signals, then the kernel will not apply default
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* signal handling behavior (which would be suspending the process) since it is
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* a member of an orphaned process group.
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*
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* Sadly this doesn't appear to be well documented except in the kernel itself:
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* https://github.com/torvalds/linux/blob/v4.2/kernel/signal.c#L2296-L2299
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*
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* Forwarding SIGSTOP instead is effective, though not ideal; unlike SIGTSTP,
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* SIGSTOP cannot be caught, and so it doesn't allow processes a change to
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* clean up before suspending. In non-setsid mode, we proxy the original signal
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* instead of SIGSTOP for this reason.
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*/
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2015-09-17 05:42:09 +03:00
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void handle_signal(int signum) {
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DEBUG("Received signal %d.\n", signum);
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2015-09-19 07:59:31 +03:00
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if (
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signum == SIGTSTP || // tty: background yourself
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signum == SIGTTIN || // tty: stop reading
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signum == SIGTTOU // tty: stop writing
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) {
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if (use_setsid) {
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DEBUG("Running in setsid mode, so forwarding SIGSTOP instead.\n");
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forward_signal(SIGSTOP);
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} else {
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DEBUG("Not running in setsid mode, so forwarding the original signal (%d).\n", signum);
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forward_signal(signum);
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}
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DEBUG("Suspending self due to TTY signal.\n");
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kill(getpid(), SIGSTOP);
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} else {
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forward_signal(signum);
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}
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2015-09-05 01:19:17 +03:00
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}
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2015-08-07 00:24:27 +03:00
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void print_help(char *argv[]) {
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2015-08-10 19:32:56 +03:00
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fprintf(stderr,
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2015-10-02 23:31:35 +03:00
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"dumb-init v%s"
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"Usage: %s [option] command [[arg] ...]\n"
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2015-08-10 19:32:56 +03:00
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"\n"
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2015-10-02 23:31:35 +03:00
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"dumb-init is a simple process supervisor that forwards signals to children.\n"
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"It is designed to run as PID1 in minimal container environments.\n"
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2015-09-04 20:26:47 +03:00
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"\n"
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2015-10-02 23:31:35 +03:00
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"Optional arguments:\n"
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" -c, --single-child Run in single-child mode.\n"
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" In this mode, signals are only proxies to the\n"
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2015-10-03 08:28:40 +03:00
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" direct child and not any of its descendants.\n"
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2015-10-02 23:31:35 +03:00
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" -v, --verbose Print debugging information to stderr.\n"
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" -h, --help Print this help message and exit.\n"
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" -V, --version Print the current version and exit.\n"
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2015-08-10 19:32:56 +03:00
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"\n"
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2015-10-02 23:31:35 +03:00
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"Full help is available online at https://github.com/Yelp/dumb-init\n",
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VERSION,
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2015-08-10 19:32:56 +03:00
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argv[0]
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);
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2015-08-07 00:24:27 +03:00
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}
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2015-07-30 02:03:55 +03:00
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int main(int argc, char *argv[]) {
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2015-10-02 23:31:35 +03:00
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int signum, opt;
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struct option long_options[] = {
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{"help", no_argument, NULL, 'h'},
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{"single-child", no_argument, NULL, 'c'},
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{"verbose", no_argument, NULL, 'v'},
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{"version", no_argument, NULL, 'V'},
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};
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while ((opt = getopt_long(argc, argv, "+hvVc", long_options, NULL)) != -1) {
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switch (opt) {
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case 'h':
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print_help(argv);
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return 0;
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case 'v':
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debug = 1;
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break;
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case 'V':
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fprintf(stderr, "dumb-init v%s", VERSION);
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return 0;
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case 'c':
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use_setsid = 0;
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break;
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default:
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return 1;
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}
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}
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2015-07-30 02:03:55 +03:00
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2015-10-02 23:31:35 +03:00
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if (optind >= argc) {
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fprintf(
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stderr,
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"Usage: %s [option] program [args]\n"
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"Try %s --help for full usage.\n",
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argv[0], argv[0]
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);
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2015-08-10 19:32:56 +03:00
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return 1;
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}
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2015-10-02 23:31:35 +03:00
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char **cmd = &argv[optind];
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2015-07-30 02:03:55 +03:00
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2015-10-02 23:31:35 +03:00
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char *debug_env = getenv("DUMB_INIT_DEBUG");
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2015-08-26 19:05:54 +03:00
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if (debug_env && strcmp(debug_env, "1") == 0) {
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2015-08-10 19:32:56 +03:00
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debug = 1;
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2015-08-26 19:05:54 +03:00
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DEBUG("Running in debug mode.\n");
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}
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2015-07-30 02:03:55 +03:00
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2015-10-02 23:31:35 +03:00
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char *setsid_env = getenv("DUMB_INIT_SETSID");
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2015-09-11 00:05:05 +03:00
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if (setsid_env && strcmp(setsid_env, "0") == 0) {
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use_setsid = 0;
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DEBUG("Not running in setsid mode.\n");
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2015-08-26 19:05:54 +03:00
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}
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2015-07-30 02:03:55 +03:00
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2015-08-10 19:32:56 +03:00
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/* register signal handlers */
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for (signum = 1; signum < 32; signum++) {
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if (signum == SIGKILL || signum == SIGSTOP || signum == SIGCHLD)
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continue;
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2015-07-30 02:03:55 +03:00
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2015-09-17 05:42:09 +03:00
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if (signal(signum, handle_signal) == SIG_ERR) {
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2015-10-02 20:48:23 +03:00
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PRINTERR("Couldn't register signal handler for signal `%d`. Exiting.\n", signum);
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2015-08-10 19:32:56 +03:00
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return 1;
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}
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}
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2015-07-30 02:03:55 +03:00
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2015-08-10 19:32:56 +03:00
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/* launch our process */
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2015-09-05 01:19:17 +03:00
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child_pid = fork();
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2015-07-30 02:03:55 +03:00
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2015-09-05 01:19:17 +03:00
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if (child_pid < 0) {
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2015-10-02 20:48:23 +03:00
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PRINTERR("Unable to fork. Exiting.\n");
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2015-08-10 19:32:56 +03:00
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return 1;
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}
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2015-07-30 02:03:55 +03:00
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2015-09-05 01:19:17 +03:00
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if (child_pid == 0) {
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2015-09-11 00:05:05 +03:00
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if (use_setsid) {
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2015-09-10 01:05:34 +03:00
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pid_t result = setsid();
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if (result == -1) {
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2015-10-02 20:48:23 +03:00
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PRINTERR(
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2015-09-11 00:05:05 +03:00
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"Unable to setsid (errno=%d %s). Exiting.\n",
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2015-08-26 19:05:54 +03:00
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errno,
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strerror(errno)
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);
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exit(1);
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}
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2015-09-11 00:05:05 +03:00
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DEBUG("setsid complete.\n");
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2015-08-26 19:05:54 +03:00
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}
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2015-10-02 23:31:35 +03:00
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execvp(cmd[0], &cmd[0]);
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2015-09-29 20:33:26 +03:00
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// if this point is reached, exec failed, so we should exit nonzero
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2015-10-02 20:48:23 +03:00
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PRINTERR("%s: %s\n", argv[1], strerror(errno));
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2015-09-29 20:33:26 +03:00
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exit(2);
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2015-08-10 19:32:56 +03:00
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} else {
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2015-09-17 05:42:09 +03:00
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pid_t killed_pid;
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int exit_status, status;
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2015-09-05 01:19:17 +03:00
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DEBUG("Child spawned with PID %d.\n", child_pid);
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2015-09-17 05:42:09 +03:00
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while ((killed_pid = waitpid(-1, &status, 0))) {
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exit_status = WEXITSTATUS(status);
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DEBUG("A child with PID %d exited with exit status %d.\n", killed_pid, exit_status);
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if (killed_pid == child_pid) {
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// send SIGTERM to any remaining children
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forward_signal(SIGTERM);
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DEBUG("Child exited with status %d. Goodbye.\n", exit_status);
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exit(exit_status);
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}
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2015-09-05 01:19:17 +03:00
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}
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2015-08-10 19:32:56 +03:00
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}
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2015-07-30 02:03:55 +03:00
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2015-08-10 19:32:56 +03:00
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return 0;
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2015-07-30 02:03:55 +03:00
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}
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