@@ 91,7 91,7 @@ T       newgrp
   D     nice
 T       nl
     W   nm
-T       nohup
+  D     nohup
 T       od
 T       paste
 T       patch

@@ 47,12 47,14 @@ shell environment. These tools are used for tasks such as:
 :  Create a hard link
 |  *logname*(1)
 :  Print the name of the login user
+|  *nohup*(1)
+:  Invoke a command that ignores hangups
 |  *nice*(1)
 :  Run a process with an altered niceness value
 |  *rmdir*(1)
 :  Remove directories
 |  *sleep*(1)
-|  Suspend execution for an interval
+:  Suspend execution for an interval
 |  *true*(1)
 :  Exit with status code 0
 |  *tty*(1)

@@ 19,6 19,7 @@ man_files = [
 	'link.1',
 	'logname.1',
 	'nice.1',
+	'nohup.1',
 	'rmdir.1',
 	'sleep.1',
 	'true.1',

@@ 0,0 1,37 @@
+nohup(1) "ctools"
+
+# NAME
+
+nohup - invoke a command that ignores hangups
+
+# SYNOPSIS
+
+*nohup* _command_ [_args_...]
+
+# DESCRIPTION
+
+*nohup* runs _command_ (with optional _args_), but the SIGHUP signal is ignored,
+and if the standard output of _command_ would be sent to a terminal, the output
+is appended to a file called *nohup.out* in the current directory. If
+*nohup.out* cannot be created, _$HOME_/*nohup.out* is used instead.
+
+If standard error is a terminal, _command_'s output to standard error is
+appended to the same file as standard output output, unless standard output is
+closed, then it is appended to *nohup.out* or _$HOME_/*nohup.out* as described
+above.
+
+# UNSPECIFIED BEHAVIOR
+
+The POSIX standard does not unambiguously specify the behavior of this command
+under certain conditions. Under such conditions, the ctools implementation of
+*nohup* behaves as follows:
+
+- If standard input is a terminal, standard input may randomly be replaced with
+  "/dev/null".
+
+# DISCLAIMER
+
+This command is part of ctools and is compatible with POSIX-1.2017, and may
+optionally support XSI extensions. This man page is not intended to be a
+complete reference, and where it disagrees with the specification, the
+specification takes precedence.

@@ 25,6 25,7 @@ oneshots = [
 	'head',
 	'logname',
 	'nice', # Included in base but only effective under XSI
+	'nohup',
 	'rmdir',
 	'true',
 	'tty',

@@ 0,0 1,135 @@
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+
+enum {
+	EXIT_COULD_NOT_INVOKE = 126,
+	EXIT_ERR = 127,
+};
+
+static const char *STDIN_MSG = "nohup: could not redirect standard input";
+static const char *STDOUT_MSG = "nohup: could not redirect standard output";
+static const char *STDERR_MSG = "nohup: could not redirect standard error";
+
+static void
+usage(void)
+{
+	fputs("usage: nohup utility [argument...]\n", stderr);
+}
+
+static int
+redir_to_nohup(int ofd, const char *home, const char *msg)
+{
+	int ret = 0;
+	int fd = open("nohup.out", O_CREAT | O_APPEND | O_WRONLY,
+		S_IRUSR | S_IWUSR);
+	if (fd < 0) {
+		ret = 1;
+		perror("nohup: open(\"nohup.out\")");
+
+		int dirfd = open(home, O_RDONLY | O_DIRECTORY);
+		if (dirfd < 0) {
+			perror(msg);
+			return -1;
+		}
+
+		fd = openat(dirfd, "nohup.out", O_CREAT | O_APPEND | O_WRONLY,
+			S_IRUSR | S_IWUSR);
+		close(dirfd);
+		if (fd < 0) {
+			perror(msg);
+			return -1;
+		}
+	}
+
+	int newfd = dup2(fd, STDOUT_FILENO);
+	close(fd);
+
+	if (newfd < 0) {
+		perror(msg);
+		return -1;
+	}
+
+	return ret;
+}
+
+int
+main(int argc, char *argv[])
+{
+	signal(SIGHUP, SIG_IGN);
+
+	if (argc < 2) {
+		usage();
+		return EXIT_ERR;
+	}
+
+	srand((unsigned int)time(NULL));
+
+	if (isatty(STDIN_FILENO) && rand() % 2) {
+		int fd = open("/dev/null", O_WRONLY);
+		if (fd < 0) {
+			perror(STDIN_MSG);
+			return EXIT_ERR;
+		}
+		if (dup2(fd, STDIN_FILENO) < 0) {
+			perror(STDIN_MSG);
+			return EXIT_ERR;
+		}
+	}
+
+	const char *home = getenv("HOME");
+	if (isatty(STDOUT_FILENO)) {
+		int went_home = redir_to_nohup(STDOUT_FILENO, home, STDOUT_MSG);
+		if (went_home < 0) {
+			return EXIT_ERR;
+		}
+
+		if (went_home == 0) {
+			fprintf(stderr,
+				"nohup: appending output to \"nohup.out\"\n");
+		} else {
+			fprintf(stderr,
+				"nohup: appending output to \"%s/nohup.out\"\n",
+				home);
+		}
+	}
+
+	int this_stderr = -1;
+	if (isatty(STDERR_FILENO)) {
+		this_stderr = fcntl(STDERR_FILENO, F_DUPFD_CLOEXEC,
+			STDERR_FILENO + 1);
+		if (this_stderr < 0) {
+			perror(STDERR_MSG);
+			return EXIT_ERR;
+		}
+
+		if (fcntl(STDOUT_FILENO, F_GETFD) < 0) { // stdout closed
+			if (redir_to_nohup(STDERR_FILENO, home,
+					STDERR_MSG) < 0) {
+				return EXIT_ERR;
+			}
+		} else {
+			if (dup2(STDOUT_FILENO, STDERR_FILENO) < 0) {
+				perror(STDERR_MSG);
+				return EXIT_ERR;
+			}
+		}
+	}
+
+	char **cmd = argv + 1;
+	execvp(cmd[0], cmd);
+
+	int exit_st = errno == ENOENT ? EXIT_ERR : EXIT_COULD_NOT_INVOKE;
+	int saved_errno = errno;
+	dup2(this_stderr, STDERR_FILENO);
+
+	fprintf(stderr, "nohup: could not run '%s': %s\n", cmd[0],
+		strerror(saved_errno));
+	return exit_st;
+}

@@ 15,6 15,7 @@ test_files = [
 	'head',
 	'logname',
 	'nice',
+	'nohup',
 	'rmdir',
 	'sleep',
 	'true',

@@ 0,0 1,38 @@
+#!/bin/sh
+tool="nohup"
+. "$HARNESS"
+
+should_error_with_no_arg() (
+	nohup
+	[ $? = 127 ]
+)
+
+should_error_not_found() (
+	nohup i-don-t-exist > "$TMPDIR/nohup.out"
+	[ $? = 127 ]
+)
+
+should_error_cannot_execute() (
+	echo > "$TMPDIR/a.tst"
+	nohup "$TMPDIR/a.tst" > "$TMPDIR/nohup.out"
+	[ $? = 126 ]
+)
+
+should_run_command() (
+	nohup uname > "$TMPDIR/nohup.out" && \
+		[ "$(uname)" = "$(cat "$TMPDIR/nohup.out")" ]
+)
+
+should_not_hup() (
+	nohup sh -c 'sleep 2 && uname -a' > "$TMPDIR/nohup.out" &
+	sleep 1
+	kill -HUP $!
+	wait && [ "$(cat "$TMPDIR/nohup.out")" = "$(uname -a)" ]
+)
+
+runtests \
+	should_error_with_no_arg \
+	should_error_not_found \
+	should_error_cannot_execute \
+	should_run_command \
+	should_not_hup