Improve error message when dtach can't find a pty.

Also add some documentation mentioning the devices that dtach usually
needs access to on Linux.

Bug reported by David Bremner at https://bugs.debian.org/804944

2 files changed, 8 insertions, 1 deletions

diff --git a/README b/README
index 3944f78..33c2d54 100644
--- a/README
+++ b/README
@@ -31,6 +31,10 @@ be easily portable to other variants of Unix. It currently assumes that
 the host system uses POSIX termios, and has a working forkpty function
 available.
 
+dtach may need access to various devices in the filesystem depending on what
+forkpty does. For example, dtach on Linux usually needs access to /dev/ptmx
+and /dev/pts.
+
 2. QUICK START
 
 Compiling dtach should be simple, as it uses autoconf:
diff --git a/master.c b/master.c
index 90b6683..1c41bc1 100644
--- a/master.c
+++ b/master.c
@@ -455,7 +455,10 @@ master_process(int s, char **argv, int waitattach, int statusfd)
 	{
 		if (statusfd != -1)
 			dup2(statusfd, 1);
-		printf("%s: init_pty: %s\n", progname, strerror(errno));
+		if (errno == ENOENT)
+			printf("%s: Could not find a pty.\n", progname);
+		else
+			printf("%s: init_pty: %s\n", progname, strerror(errno));
 		exit(1);
 	}