138 lines
3.9 KiB
C
138 lines
3.9 KiB
C
/*
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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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* To get debug output on stderr, run with DUMB_INIT_DEBUG=1
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*/
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#include <errno.h>
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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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#define DEBUG(...) do { \
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if (debug) { \
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fprintf(stderr, __VA_ARGS__); \
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} \
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} while (0)
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pid_t child = -1;
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char debug = 0;
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char use_process_group = 1;
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void signal_handler(int signum) {
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DEBUG("Received signal %d.\n", signum);
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if (child > 0) {
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kill(use_process_group ? -child : child, signum);
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DEBUG("Forwarded signal to child.\n");
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} else {
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DEBUG("Didn't forward signal, no child exists yet.");
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}
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}
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void print_help(char *argv[]) {
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fprintf(stderr,
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"Usage: %s COMMAND [[ARG] ...]\n"
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"\n"
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"Docker runs your processes as PID1. The kernel doesn't apply default signal\n"
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"handling to PID1 processes, so if your process doesn't register a custom\n"
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"signal handler, signals like TERM will just bounce off your process.\n"
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"\n"
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"This can result in cases where sending signals to a `docker run` process\n"
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"results in the run process exiting, but the container continuing in the\n"
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"background.\n"
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"\n"
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"A workaround is to wrap your script in this proxy, which runs as PID1. Your\n"
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"process then runs as some other PID, and the kernel won't treat the signals\n"
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"that are proxied to them specially.\n"
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"\n"
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"The proxy dies when your process dies, so it must not double-fork or do other\n"
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"weird things (this is basically a requirement for doing things sanely in\n"
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"Docker anyway).\n"
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"\n"
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"By default, dumb-init starts a process group and kills all processes in it.\n"
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"This is usually useful behavior, but if for some reason you wish to disable\n"
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"it, run with DUMB_INIT_PROCESS_GROUP=0.\n",
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argv[0]
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);
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}
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int main(int argc, char *argv[]) {
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int signum, exit_status, status = 0;
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char *debug_env, *pgroup_env;
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if (argc < 2) {
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print_help(argv);
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return 1;
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}
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debug_env = getenv("DUMB_INIT_DEBUG");
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if (debug_env && strcmp(debug_env, "1") == 0) {
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debug = 1;
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DEBUG("Running in debug mode.\n");
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}
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pgroup_env = getenv("DUMB_INIT_PROCESS_GROUP");
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if (pgroup_env && strcmp(pgroup_env, "0") == 0) {
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use_process_group = 0;
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DEBUG("Not running in process group mode.\n");
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}
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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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if (signal(signum, signal_handler) == SIG_ERR) {
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fprintf(stderr, "Error: Couldn't register signal handler for signal `%d`. Exiting.\n", signum);
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return 1;
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}
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}
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/* launch our process */
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child = fork();
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if (child < 0) {
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fprintf(stderr, "Unable to fork. Exiting.\n");
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return 1;
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}
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if (child == 0) {
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if (use_process_group) {
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pid_t result = setpgid(0, 0);
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if (result != 0) {
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fprintf(
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stderr,
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"Unable to create process group (errno=%d %s). Exiting.\n",
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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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DEBUG("Set process group ID of child to its own PID.\n");
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}
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execvp(argv[1], &argv[1]);
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} else {
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DEBUG("Child spawned with PID %d.\n", child);
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/* wait for child to exit */
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waitpid(child, &status, 0);
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exit_status = WEXITSTATUS(status);
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DEBUG("Child exited with status %d. Goodbye.\n", exit_status);
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return exit_status;
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}
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return 0;
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}
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