From 79e610fa093f2a2da29dedae6722d18178909d9f Mon Sep 17 00:00:00 2001 From: Alexander Rosenberg Date: Sat, 10 Jan 2026 02:18:04 -0800 Subject: [PATCH] Initial commit --- .gitignore | 2 + LICENSE | 674 +++++++++++++++++++++++++++++++++++++++++++ Makefile | 19 ++ README.md | 22 ++ die-with-parent.1 | 60 ++++ die-with-parent.c | 201 +++++++++++++ gen-signal-names.awk | 28 ++ 7 files changed, 1006 insertions(+) create mode 100644 .gitignore create mode 100644 LICENSE create mode 100644 Makefile create mode 100644 README.md create mode 100644 die-with-parent.1 create mode 100644 die-with-parent.c create mode 100644 gen-signal-names.awk diff --git a/.gitignore b/.gitignore new file mode 100644 index 0000000..2d4aace --- /dev/null +++ b/.gitignore @@ -0,0 +1,2 @@ +die-with-parent +signal-names.h diff --git a/LICENSE b/LICENSE new file mode 100644 index 0000000..f288702 --- /dev/null +++ b/LICENSE @@ -0,0 +1,674 @@ + GNU GENERAL PUBLIC LICENSE + Version 3, 29 June 2007 + + Copyright (C) 2007 Free Software Foundation, Inc. + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + Preamble + + The GNU General Public License is a free, copyleft license for +software and other kinds of works. + + The licenses for most software and other practical works are designed +to take away your freedom to share and change the works. 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If your program is a subroutine library, you +may consider it more useful to permit linking proprietary applications with +the library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. But first, please read +. diff --git a/Makefile b/Makefile new file mode 100644 index 0000000..97e4244 --- /dev/null +++ b/Makefile @@ -0,0 +1,19 @@ +CC=gcc +CFLAGS=-std=c11 -g +PREFIX=/usr/local + +die-with-parent: die-with-parent.c signal-names.h + $(CC) $(CFLAGS) -o die-with-parent die-with-parent.c + +signal-names.h: + awk -v COMPILER=$(CC) -f gen-signal-names.awk >$@ + +install: die-with-parent + install -Ds die-with-parent "$(PREFIX)/bin/die-with-parent" + install -Dm 0644 die-with-parent.1 \ + "$(PREFIX)/share/man/man1/die-with-parent.1" + +clean: + rm -f die-with-parent signal-names.h + +.PHONY: install clean diff --git a/README.md b/README.md new file mode 100644 index 0000000..51f11df --- /dev/null +++ b/README.md @@ -0,0 +1,22 @@ +# die-with-parent + +die-with-parent is a small program that allows you to ensure a child process +dies when its parent does, even if the parent died due to a SIGKILL. It +currently only works on Linux (though it could be easily modified to work on +other OSes in the future). + +### Building and Installation +To build, just run `make`. Install with `make install`. Optionally, +`make PREFIX=path/to/prefix install` can be used to specify an installation +prefix. + +### Usage +To use, wrap the command you want to run with `die-with-parent`: +```sh +die-with-parent your-command-here -some -cool -args +``` +to avoid race conditions (see the man page) you should pass the parent process' +PID with the `-p` flag. For example, in `sh` or `bash`: +```sh +die-with-parent -p $$ your-command-here -some -cool -args +``` diff --git a/die-with-parent.1 b/die-with-parent.1 new file mode 100644 index 0000000..f4124c2 --- /dev/null +++ b/die-with-parent.1 @@ -0,0 +1,60 @@ +.TH die-with-parent + +.Sh NAME +die-with-parent \- run a process, ensuring it dies when its parent does + +.SH SYNOPSIS +die-with-parent [\fB\-h\fR] [\fB\-s\fR \fISIGNAL\fR] [\fB\-n\fR] \ +[\fB\-p \fIPID\fR] \fICOMMAND\fR \fIARGS\fR... + +.SH DESCRIPTION +\fBdie-with-parent\fR executes a program and arranges for that program to revive a +signal if its parent dies before it does. On Linux (the only operating system +currently supported), this is accomplished via the \fIprctl\fP(2) system-call using +\fIPR_SET_PDEATHSIG\fP(2). + +To prevent race conditions, the parent should pass its PID the the \fB\-p\fR +flag. After the child finishes setting up, it will check if its parent's PID has +changed. If it has, this mean the parent exited and the child was reparented. If +this happens, the child will signal itself with \fIraise\fP(3). + +.SH OPTIONS +.TP +.B \-h +Print a help message, then exit +.TP +.B \-s \fISIGNAL\fR +Specify the signal to send when the parent dies (default: SIGHUP) +.TP +.B \-n +treat \fICOMMAND\fR as a file path, not a command name (ignore $PATH) +.TP +.B \-p \fIPID\fR +specify the parent processes process-id as PID + +.SH SIGNAL FORMAT +Signals can be passed to the \fB\-s\fR option either by number or by name. When +passed by number, the signal should be an unsigned integer. When passed by name, +the signal's abbriviated name should be used. This name can optionally be +prefixed by "SIG". For example, signal 9 can also be represented as SIGKILL or +just KILL. Therefore "-s KILL", "-s SIGKILL", and "-s 9" are all +equivalent. Finally, real-time signals can either be represented by number or in +the form of "RTMIN+X" or "SIGRTMIN+X" where X is the offset from the smallest +real-time signal. You can also go the other direction with "RTMAX-X". + +The actual names available depend on your system. At build time, system headers +are scanned and the resultant list is compiled into \fBdie-with-parent\fR. + +.SH BUGS +There is a race condition that will occur if the parent process dies before the +child process is able to call \fIprctl\fP(2). This can be avoided by use of the +\fB\-p\fR option. + +.SH SEE ALSO +\fIprctl\fP(2), \fIPR_SET_PDEATHSIG\fP(2), \fIsignal\fP(7) + +.SH COPYING +\fBdie-with-parent\fR is free software under the terms of the GNU Public License +version 3 or later. You should have revived a copy of the license text with this +software. If not, you can find the full license text at +https://www.gnu.org/licenses/gpl-3.0.en.html. diff --git a/die-with-parent.c b/die-with-parent.c new file mode 100644 index 0000000..c1268de --- /dev/null +++ b/die-with-parent.c @@ -0,0 +1,201 @@ +#define _XOPEN_SOURCE +#define _POSIX_C_SOURCE 200112L +#include "signal-names.h" + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#define PID_MAX ((((size_t) 1) << (sizeof(pid_t) * 8)) + 1) + +static const char *EXEC_NAME; + +int eprintf(const char *fmt, ...) { + va_list args; + va_start(args, fmt); + int c = 0; + c += fprintf(stderr, "%s: ", EXEC_NAME); + c += vfprintf(stderr, fmt, args); + c += fputc('\n', stderr); + va_end(args); + return c; +} + +/* + * Arrange for the current process to be sent SIGNAL when its parent dies. + * This should return false on error and print a diagnostic message. + */ +bool die_with_parent(int signal); + +#ifdef __linux__ +# include +# include + +bool die_with_parent(int signal) { + if (prctl(PR_SET_PDEATHSIG, signal) < 0) { + eprintf("prctl PR_SET_PDEATHSIG: %s", strerror(errno)); + return false; + } + return true; +} +#else +# error "Unsuported operating system" +#endif + +/* + * Parse OPT into an integer signal number, or return -1 on error. + */ +int parse_signal(const char *opt) { + if (*opt >= '0' && *opt <= '9') { + char *endptr; + long signum = strtol(opt, &endptr, 10); + if (*endptr) { + return -1; + } + return signum; + } else if (strncasecmp(opt, "SIG", 3) == 0) { + opt += 3; + } + if (strncasecmp(opt, "RT", 2) == 0) { + int reference = 0; + if (strncasecmp(opt + 2, "MIN", 3) == 0) { + reference = SIGRTMIN; + } else if (strncasecmp(opt + 2, "MAX", 3) == 0) { + reference = SIGRTMAX; + } + if (reference > 0) { + if (!opt[5]) { + return reference; + } + char *endptr; + long signum = strtol(opt + 5, &endptr, 10); + if ((signum > 0 && reference != SIGRTMIN) + || (signum < 0 && reference != SIGRTMAX)) { + return -1; + } + long abs_signum = signum < 0 ? -signum : signum; + return !*endptr && abs_signum <= SIGRTMAX - SIGRTMIN + ? reference + signum + : -1; + } + } + for (size_t i = 0; i < MAX_SIGNUM; ++i) { + if (SIGNAL_NAMES[i] && strcasecmp(opt, SIGNAL_NAMES[i] + 3) == 0) { + return i; + } + } + return -1; +} + +void print_help(FILE *stream) { + fprintf(stream, + "usage: %s [-h] [-s SIGNAL] [-n] [-p PID] COMMAND ARGS...\n", + EXEC_NAME); + fprintf(stream, "Arrange for COMMAND to be executed with ARGS, arranging " + "for it to have a signal\nsent when its parent dies.\n\n"); + fprintf(stream, "Options:\n"); + fprintf(stream, " -h print this message, then exit\n"); + fprintf( + stream, + " -s arrage for SIGNAL to be sent instead of the default SIGHUP\n"); + fprintf(stream, " -n don't search $PATH for COMMAND\n"); + fprintf(stream, " -p specify the parent processes process-id as PID\n"); +} + +int main(int argc, char *const *argv) { + EXEC_NAME = argv[0]; + opterr = false; + int signal_num = SIGHUP; + bool no_search = false; + bool had_error = false; + pid_t init_ppid = -1; + int c; + const char *old_posixly_correct = getenv("POSIXLY_CORRECT"); + putenv("POSIXLY_CORRECT=1"); + while ((c = getopt(argc, argv, ":hs:np:")) >= 0) { + switch (c) { + case 'h': + print_help(stdout); + return 0; + case 's': + signal_num = parse_signal(optarg); + if (signal_num < 0) { + eprintf("unknown signal: %s", optarg); + had_error = true; + } + break; + case 'n': + no_search = true; + break; + case 'p': { + char *endptr; + long lpid = strtol(optarg, &endptr, 10); + if (!endptr) { + eprintf("invalid pid: %s", optarg); + had_error = true; + } else if (lpid < 1 || lpid > PID_MAX) { + eprintf("out of range: %s", optarg); + had_error = true; + } + init_ppid = lpid; + } break; + case ':': + if (isprint(optopt)) { + eprintf("option requires argument: -%c", optopt); + } else { + eprintf("option requires argument: 0x%x", optopt); + } + had_error = true; + break; + case '?': + if (isprint(optopt)) { + eprintf("unknown option: -%c", optopt); + } else { + eprintf("unknown option: 0x%x", optopt); + } + break; + } + } + if (!argv[optind]) { + eprintf("expected command as positional arguments"); + return 1; + } + if (!old_posixly_correct) { + unsetenv("POSIXLY_CORRECT"); + } else { + setenv("POSIXLY_CORRECT", old_posixly_correct, true); + } + if (had_error) { + return 1; + } + if (!die_with_parent(signal_num)) { + return 1; + } + // we now check if the parent exited before this point + pid_t new_ppid = getppid(); + if (new_ppid != init_ppid) { + raise(signal_num); + // if we got here that means the signal in question was ignored which is + // probably what the user intended, so just go on with execing the new + // process + } + const char *func; + if (no_search) { + execv(argv[optind], &argv[optind]); + func = "execv"; + } else { + execvp(argv[optind], &argv[optind]); + func = "execvp"; + } + // if we got here it means an error occurred + eprintf("%s: %s", func, strerror(errno)); + return 1; +} diff --git a/gen-signal-names.awk b/gen-signal-names.awk new file mode 100644 index 0000000..f2b3153 --- /dev/null +++ b/gen-signal-names.awk @@ -0,0 +1,28 @@ +BEGIN { + cmd = "printf '#include \n' | " COMPILER " -E -dM -x c - | sort -nk 3" + FS=" " + print "#include " + print "" + print "static const char *SIGNAL_NAMES[] = {" + min = 0 + max = 0 + while ((cmd | getline record)) { + if (record ~ /^#define\s*SIG[A-Z0-9]+\s*[0-9]+$/) { + split(record, fields, /\s+/) + name = fields[2] + number = fields[3] + if (name != "SIGSTKSZ") { + print " [" name "] = \"" name "\"," + if (min == 0) { + min = number + } + if (number > max) { + max = number + } + } + } + } + print "};" + print "#define MIN_SIGNUM " min + print "#define MAX_SIGNUM " max +}