Add nologin(8)

Signed-off-by: Mattias Andrée <maandree@kth.se>

Makefile

@@ -64,6 +64,7 @@ BIN = \
 	mkswap            \
 	mount             \
 	mountpoint        \
+	nologin           \
 	pagesize          \
 	passwd            \
 	pidof             \
@@ -129,6 +130,7 @@ MAN8 = \
 	lsusb.8             \
 	mkswap.8            \
 	mount.8             \
+	nologin.8           \
 	pivot_root.8        \
 	readahead.8         \
 	rmmod.8             \

nologin.8

@@ -0,0 +1,21 @@
+.Dd March 26, 2016
+.Dt NOLOGIN 8
+.Os ubase
+.Sh NAME
+.Nm nologin
+.Nd refuse login
+.Sh SYNOPSIS
+.Nm
+.Sh DESCRIPTION
+.Nm
+prints a message informing the user that she
+is not allowed to log in. If /etc/nologin.txt
+exists, its content is printed instead of
+the default message.
+.Pp
+.Nm
+is intended to be specified as the user's
+default shell.
+.Sh EXIT STATUS
+.Nm
+returns a status code indicating failure.

nologin.c

@@ -0,0 +1,22 @@
+/* See LICENSE file for copyright and license details. */
+#include <stdio.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+int
+main(void)
+{
+	int fd;
+	char buf[BUFSIZ];
+	ssize_t n;
+
+	fd = open("/etc/nologin.txt", O_RDONLY);
+	if (fd >= 0) {
+		while ((n = read(fd, buf, sizeof(buf))) > 0)
+			write(STDOUT_FILENO, buf, n);
+		close(fd);
+	} else {
+		printf("The account is currently unavailable.\n");
+	}
+	return 1;
+}