DVTM – dynamic virtual terminal manager

Monday, February 11th, 2008

I do a lot of remote UNIX administration on various servers and even some desktop machines. This usually means that I’m doing a lot of SSHing into machines, often opening multiple sessions to the same machine at the same time. It quickly becomes tedious to keep having to type ‘ssh fboender@some.machine.com‘ four times in order to get four sessions.

Of course there is Screen, but Screen’s split screen abilities are very limited and don’t really work for me. While scanning Freshmeat.net, I found a tool called DVTM: dynamic virtual terminal manager.

DVTM is a kind of window manager for the console (or xterm) which allows you to quite easily split your terminal into multiple split screens.

DVTM has some limitations though:

Configuration is done using C code. (Though you’ll probably never need to change anything; the defaults are quite sane)
It doesn’t seem to support ANSI colouring. I use a red background at my prompt when I’m root, which I now have to miss.
It also doesn’t seem to support line-drawing. This probably has something to do with the terminal type.
DVTM has no internal support for detaching and reattaching to running DVTM instances like Screen can. (But see the Tips and tricks section on the homepage).
There are a couple of small bugs, one of which is a problem with repeating keys when switching between split windows with the mouse.

But make no mistake: despite these shortcomings, DVTM is an absolutely fantastic tool. Some of the neat stuff it supports is:

Mouse support for switching between split windows / maximizing and unmaximizing, etc.
Maximize/unmaximize the currently active window (Default: Ctrl-g m / Ctrl-g g)
Various window layouts (you can probably add your own by hacking the source code)
Almost no dependencies except for ncurses.

The only thing I’d really like to see changed about DVTM are custom run-time splitting (for instance, Ctrl-g-MINUS to split the current window horizontally and Ctrl-g-PIPE to split the window vertically) and detaching/reattaching.

All in all, DVTM is an awesome tool. Go download it if you do a lot of remote administration.

Update: There also appear to be two bugs:

On the latest Ubuntu: Sometimes when exiting DVTM, it will hang for a while, and the cursor will blink like mad. An strace shows that IO Errors are occuring on file descriptor 3. I’ve filed a bug report with the author. This bug doesn’t appear on Debian stable.
When using DVTM in combination with dtach, reattaching doesn’t redraw the screen. This appears to be a problem with DVTM, but it would probably be easier to solve in dtach (which could just signal a screen resize event without actually resizing the screen). This is also the workaround for this bug: just resize the window. I’ll see if I can file a bug report with either DVTM’s author or dtach’s author.

Update II: Here’s a little patch/workaround for the first bug (exiting DVTM hangs for a while):

--- dvtm.c      2008-02-06 17:30:25.000000000 +0100
+++ ../dvtm-0.4/dvtm.c  2008-02-11 23:33:45.000000000 +0100
@@ -896,6 +896,7 @@
                Client *c;
                int r, nfds = 0;
                fd_set rd;
+               struct timeval tv;
 
                if(need_screen_resize)
                        resize_screen();
@@ -996,6 +997,13 @@
                        wnoutrefresh(sel->window);
                }
                doupdate();
+
+               // One microsecond delay so this loop doesn't hang context-switching
+               // when the last child dies and the SIGCHLD signal is prevented from
+               // being caught on time.
+               tv.tv_sec = 0;
+               tv.tv_usec = 1;
+               select(0, NULL, NULL, NULL, &tv);
        }
 
        cleanup();

Save to ~/patch.diff and in the dvtm-0.4 directory run:

~/dvtm-0.4$ patch -p0 < ~/patch.diff

Update III:

I was incorrect in stating that dvtm doesn't support ANSI coloring. It's just the bash prompt which doesn't work. Perhaps because there is a Xterm-styled window title ANSI sequence in there. Will update when I know more.

Update IV:

Marginally better patch:

diff -Naur ./dvtm.c ../dvtm-0.4/dvtm.c
--- ./dvtm.c	2008-02-06 17:30:25.000000000 +0100
+++ ../dvtm-0.4/dvtm.c	2008-02-12 22:08:54.000000000 +0100
@@ -982,7 +982,10 @@
 
 		for(c = clients; c; c = c->next){
 			if(FD_ISSET(c->pty, &rd)){
-				madtty_process(c->term);
+				if (madtty_process(c->term) < 0 && errno == EIO) {
+					/* client probably terminated */
+					client_killed = c;
+				}
 				if(c != sel){
 					draw_content(c);
 					if(!isarrange(fullscreen))

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DVTM – dynamic virtual terminal manager