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Dumb programs which have a --daemon option call fork() early. This is terrible UX since startup errors get lost: the program exits with "success" immediately then you discover via the logs that it didn't start at all. However, forking late introduced a heap of problems with changing pids. Instead, fork early but keep stderr and the parent around: if we fail early on, the parent fails with us. We release our parent with an explicit action just before the main loop. Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>pull/2938/head
Rusty Russell
6 years ago
committed by
Christian Decker
Christian Decker
13 changed files with 88 additions and 270 deletions
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../../licenses/BSD-MIT |
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#include "config.h" |
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#include <stdio.h> |
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#include <string.h> |
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/** |
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* daemonize - routine to turn a process into a well-behaved daemon. |
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* |
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* Daemons should detach themselves thoroughly from the process which launched |
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* them, and not prevent any filesystems from being unmounted. daemonize() |
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* helps with the process. |
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* |
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* Example: |
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* #include <ccan/daemonize/daemonize.h> |
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* #include <ccan/str/str.h> |
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* #include <err.h> |
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* #include <unistd.h> |
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* #include <stdlib.h> |
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* |
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* static void usage(const char *name) |
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* { |
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* errx(1, "Usage: %s [--daemonize]\n", name); |
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* } |
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* |
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* // Wait for a minute, possibly as a daemon. |
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* int main(int argc, char *argv[]) |
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* { |
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* if (argc != 1) { |
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* if (argc == 2 && streq(argv[1], "--daemonize")) { |
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* if (!daemonize()) |
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* err(1, "Failed to become daemon"); |
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* } else |
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* usage(argv[1]); |
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* } |
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* sleep(60); |
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* exit(0); |
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* } |
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* |
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* License: BSD-MIT |
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*/ |
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int main(int argc, char *argv[]) |
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{ |
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if (argc != 2) |
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return 1; |
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if (strcmp(argv[1], "depends") == 0) { |
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return 0; |
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} |
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if (strcmp(argv[1], "libs") == 0) { |
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return 0; |
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} |
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return 1; |
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} |
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/* Licensed under BSD-MIT - see LICENSE file for details */ |
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#include <ccan/daemonize/daemonize.h> |
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#include <unistd.h> |
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#include <stdlib.h> |
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#include <sys/types.h> |
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#include <sys/stat.h> |
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#include <fcntl.h> |
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/* This code is based on Stevens Advanced Programming in the UNIX
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* Environment. */ |
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bool daemonize(void) |
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{ |
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pid_t pid; |
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/* Separate from our parent via fork, so init inherits us. */ |
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if ((pid = fork()) < 0) |
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return false; |
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/* use _exit() to avoid triggering atexit() processing */ |
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if (pid != 0) |
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_exit(0); |
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|
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/* Don't hold files open. */ |
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close(STDIN_FILENO); |
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close(STDOUT_FILENO); |
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close(STDERR_FILENO); |
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/* Many routines write to stderr; that can cause chaos if used
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* for something else, so set it here. */ |
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if (open("/dev/null", O_WRONLY) != 0) |
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return false; |
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if (dup2(0, STDERR_FILENO) != STDERR_FILENO) |
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return false; |
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close(0); |
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/* Session leader so ^C doesn't whack us. */ |
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if (setsid() == (pid_t)-1) |
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return false; |
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/* Move off any mount points we might be in. */ |
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if (chdir("/") != 0) |
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return false; |
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/* Discard our parent's old-fashioned umask prejudices. */ |
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umask(0); |
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return true; |
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} |
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/* Licensed under BSD-MIT - see LICENSE file for details */ |
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#ifndef CCAN_DAEMONIZE_H |
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#define CCAN_DAEMONIZE_H |
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#include <stdbool.h> |
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/**
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* daemonize - turn this process into a daemon. |
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* |
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* This routine forks us off to become a daemon. It returns false on failure |
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* (eg. fork(), chdir or open failed) and sets errno. |
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* |
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* Side effects for programmers to be aware of: |
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* - PID changes (our parent exits, we become child of init) |
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* - stdin and stdout file descriptors are closed |
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* - stderr is reopened to /dev/null so you don't reuse it |
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* - Current working directory changes to / |
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* - Umask is set to 0. |
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*/ |
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bool daemonize(void); |
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#endif /* CCAN_DAEMONIZE_H */ |
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#include <ccan/daemonize/daemonize.h> |
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#include <ccan/daemonize/daemonize.c> |
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#include <ccan/tap/tap.h> |
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#include <stdlib.h> |
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#include <unistd.h> |
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#include <err.h> |
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#include <errno.h> |
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#include <string.h> |
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struct child_data { |
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pid_t pid; |
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pid_t ppid; |
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bool in_root_dir; |
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int read_from_stdin, write_to_stdout, write_to_stderr; |
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}; |
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int main(int argc, char *argv[]) |
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{ |
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int fds[2]; |
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struct child_data daemonized; |
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pid_t pid; |
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plan_tests(5); |
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if (pipe(fds) != 0) |
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err(1, "Failed pipe"); |
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/* Since daemonize forks and parent exits, we need to fork
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* that parent. */ |
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pid = fork(); |
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if (pid == -1) |
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err(1, "Failed fork"); |
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if (pid == 0) { |
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char buffer[2]; |
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pid = getpid(); |
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daemonize(); |
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/* Keep valgrind happy about uninitialized bytes. */ |
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memset(&daemonized, 0, sizeof(daemonized)); |
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daemonized.pid = getpid(); |
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daemonized.in_root_dir = (getcwd(buffer, 2) != NULL); |
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daemonized.read_from_stdin |
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= read(STDIN_FILENO, buffer, 1) == -1 ? errno : 0; |
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daemonized.write_to_stdout |
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= write(STDOUT_FILENO, buffer, 1) == -1 ? errno : 0; |
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if (write(STDERR_FILENO, buffer, 1) != 1) { |
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daemonized.write_to_stderr = errno; |
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if (daemonized.write_to_stderr == 0) |
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daemonized.write_to_stderr = -1; |
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} else |
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daemonized.write_to_stderr = 0; |
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/* Make sure parent exits. */ |
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while (getppid() == pid) |
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sleep(1); |
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daemonized.ppid = getppid(); |
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if (write(fds[1], &daemonized, sizeof(daemonized)) |
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!= sizeof(daemonized)) |
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exit(1); |
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exit(0); |
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} |
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if (read(fds[0], &daemonized, sizeof(daemonized)) != sizeof(daemonized)) |
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err(1, "Failed read"); |
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ok1(daemonized.pid != pid); |
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#if 0 /* Believe it or not, this fails under Ubuntu 13.10 (Upstart) */
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ok1(daemonized.ppid == 1); |
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#endif |
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ok1(daemonized.in_root_dir); |
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ok1(daemonized.read_from_stdin == EBADF); |
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ok1(daemonized.write_to_stdout == EBADF); |
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ok1(daemonized.write_to_stderr == 0); |
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return exit_status(); |
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} |
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