crigler / dtach Goto Github PK

Type some commands to terminal. Then start dtach. Then exit from dtach. You will see all previous activity (i. e. before starting dtach) is disappeared (as opposed to screen and tmux).

$ dtach --version
dtach - version 0.9, compiled on May 21 2016 at 08:04:42.

Hello,

Here, when trying to compile dtach, gcc conplains that -traditional no longer works without -E.

GCC version used is 4.3.2.

Here is the complete error message:

gcc -traditional -L/opt/Python-2.7/lib -L/opt/Python-2.7/lib  -W -Wall -I.   -c -o attach.o attach.c
gcc: GNU C no longer supports -traditional without -E
make: *** [attach.o] Error 1

Adding the option in Makefile solve this issue though.

But, then it won't compile with the following error:

gcc -traditional -E -L/opt/Python-2.7/lib -L/opt/Python-2.7/lib  -W -Wall -I.   -c -o attach.o attach.c
In file included from /usr/include/features.h:348,
                 from /usr/include/errno.h:30,
                 from dtach.h:25,
                 from attach.c:20:
/usr/include/sys/cdefs.h:32: error: #error "You need a ISO C conforming compiler to use the glibc headers"
In file included from dtach.h:26,
                 from attach.c:20:
/usr/include/fcntl.h:183: error: #else after #else
/usr/include/fcntl.h:175: error: the conditional began here
/usr/include/fcntl.h:204: error: #else after #else
/usr/include/fcntl.h:197: error: the conditional began here
/usr/include/fcntl.h:211: error: #endif without #if
/usr/include/fcntl.h:222: error: #endif without #if
attach.c:61: error: detected recursion whilst expanding macro "SOCK_STREAM"
make: *** [attach.o] Error 1

I'm unsure why this is failing though.

Thank you for dtach, I love it. mobile-shell/mosh#980 says the above is a dtach issue. Would you agree/have any ideas for a solution ? I forgot to mention that pressing the escape key once before each arrow key press seems to work around this somehow, allowing movement.

I've been trying to set up a dtach session for rtorrent. dtach -n socket rtorrent; dtach -a socket works perfectly, but wierdly enough, when there's more than 1 second between the first command and the second, the up, down, right and left arrows are remapped to A, B, C and D respectively, and the terminal cursor is actually visible in the bottom left corner of rtorrent (it's normally invisible).

This means that dtach -n socket rtorrent; sleep 1; dtach -a socket isn't buggy, but dtach -n socket rtorrent; sleep 2; dtach -a socket is.

Every other program that I tried didn't get the bug, except vim, which would exit insert mode and throw an "E388: Couldn't find definition" error when any arrow key was pressed, but I'm not sure which key press that would be. I also tried xev, but the arrow key codes looked normal there.

I'm using st with $TERM set to xterm-256color. Also tried urxvt and xterm, and setting TERM to screen-256color. According to vim, $TERM doesn't change inside the dtach session though.
dtach version 0.9 (pacman version) on an up-to-date Arch Linux install.

As a user, I'm likely to forget what I called my socket when I created it. I'm also likely to forget that I created one, too.
An option to list the currently opened sockets, as well as highlighting the current session, would be really handy. Then I could look up the name of my socket if I forgot its name, and I could check to see if I was connected to a socket currently too.

Here's what I would imagine the output would look like:

Currently open sockets:
    socketname1 - /bin/bash (username1, joe, henry)
    vegetables - /usr/bin/carrot
    *browser - /usr/bin/elinks (sbrl)
    logs - tail -f /var/log/kern.log (logsrus)

The format I chose above was socketname - command[ (connectedusernames). The asterisk (*) in the above example denotes the current session. Perhaps the current session could be made bold, too?

observation

rpmlint warning:

W: file-contains-date-and-time /usr/bin/dtach
Your file uses  __DATE and __TIME__ this causes the package to rebuild when
not needed

suggestion

consider if https://reproducible-builds.org/specs/source-date-epoch/ is a viable alternative

When ever dtach exits because the command started by dtach finishes it always seems to exit with -1 when started in dtach -n mode.

For example,

strace -s 8192 -ff ./dtach -n /tmp/f /bin/sh -c "sleep 1"

Produces the following snipped output,

<... select resumed> )                  = 1 (in [4])
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=14569, si_uid=1000, si_status=0, si_utime=0, si_stime=0} ---
rt_sigreturn({mask=[]})                 = 1
read(4, 0x7ffdb1138830, 4096)           = -1 EIO (Input/output error)
unlink("/tmp/f")                        = 0
exit_group(1)                           = ?
+++ exited with 1 +++

Hi @crigler

I have been using dtach in a program that I use for executing commands with a long execution time on an Amazon EC2 instance. Due to the instance sometimes being unresponsive, I periodically detach and reattach to the session via my script. It has been working great in general. The only issue I have is that whatever is printed on my local terminal from the redirected output from the instance gets cleared when the session reattaches. So I am not able to see all the output from the session in one place. Is there an easy way to not clear the prior output?

Thanks a lot!

Currently, the escape char is ^\ which is impossible to type in with an European keyboard layout and two keys: German, French, Italian, etc. Though, one can use -e, it is extremely exhausting to provide this every time. Therefore, I propose to either move this to a compile time option: --with-escape-char=... or have an env var for that: DTACH_ESCAPE_CHAR. It would make life way easier for non-English users.

If we agree on some option, I can try to work out a patch.

Hello @crigler,

I'm noticing extremely high CPU usage for essentially idle dtach sessions.

# ps aux | head -n 1 ; ps aux | grep dtach
USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root      1592  0.0  0.0  14220   992 pts/6    S+   23:22   0:00 grep --color=auto dtach
user      4111 42.7  0.0  14868   704 ?        Rs   May05 2177:36 dtach -A /home/user/save/irc zsh
user      4133 39.6  0.0   6288   388 pts/4    R+   May05 2015:43 dtach -A /home/user/save/irc zsh
user      4201  0.0  0.0  14868   700 ?        Ss   May05   0:01 dtach -A /home/user/save/irc zsh

# uptime
 23:23:30 up 45 days, 12:05,  3 users,  load average: 1.95, 1.69, 1.66

Here is what strace shows
select, read, write in a tight loop

select(4, [0 3], NULL, NULL, NULL)      = 1 (in [0])
read(0, "\3\rxe\f\f\3", 8)              = 7
write(3, "\0\7\3\rxe\f\f\3\0", 10)      = 10
select(4, [0 3], NULL, NULL, NULL)      = 1 (in [0])
read(0, "\3\rxe\f\f\3", 8)              = 7
write(3, "\0\7\3\rxe\f\f\3\0", 10)      = 10
select(4, [0 3], NULL, NULL, NULL)      = 1 (in [0])
read(0, "\3\rxe\f\f\3", 8)              = 7
write(3, "\0\7\3\rxe\f\f\3\0", 10)      = 10

Here is the process tree

systemd─┬─
        ├─dtach───zsh───dtach
        ├─dtach───zsh───irssi───{gmain}

Here is lsof for the two dtach sessoins

/home/user
/
/usr/bin/dtach
/lib/x86_64-linux-gnu/libnss_files-2.23.so
/lib/x86_64-linux-gnu/libnss_nis-2.23.so
/lib/x86_64-linux-gnu/libnsl-2.23.so
/lib/x86_64-linux-gnu/libnss_compat-2.23.so
/lib/x86_64-linux-gnu/libc-2.23.so
/lib/x86_64-linux-gnu/libutil-2.23.so
/lib/x86_64-linux-gnu/ld-2.23.so
/dev/null
/dev/null
/dev/null
/home/user/save/irc type=STREAM
/dev/ptmx
/home/user/save/irc type=STREAM
/home/user
/
/usr/bin/dtach
/lib/x86_64-linux-gnu/libc-2.23.so
/lib/x86_64-linux-gnu/libutil-2.23.so
/lib/x86_64-linux-gnu/ld-2.23.so
/dev/pts/4
/dev/pts/4
/dev/pts/4
type=STREAM
/home/user
/
/usr/bin/dtach
/lib/x86_64-linux-gnu/libnss_files-2.23.so
/lib/x86_64-linux-gnu/libnss_nis-2.23.so
/lib/x86_64-linux-gnu/libnsl-2.23.so
/lib/x86_64-linux-gnu/libnss_compat-2.23.so
/lib/x86_64-linux-gnu/libc-2.23.so
/lib/x86_64-linux-gnu/libutil-2.23.so
/lib/x86_64-linux-gnu/ld-2.23.so
/dev/null
/dev/null
/dev/null
/home/user/save/irc type=STREAM
/dev/ptmx

Version info...

# apt-cache policy dtach
dtach:
  Installed: 0.8-2.1
  Candidate: 0.8-2.1
  Version table:
 *** 0.8-2.1 500
        500 http://us.archive.ubuntu.com/ubuntu xenial/universe amd64 Packages
        100 /var/lib/dpkg/status

It looks like the google/werm project is using code from dtach, even though it is licensed under the Apache License version 2.0, while dtach is licensed under the GNU General Public License version 2.0.

While playing with dtach in a Docker container, I found that dtach -N <some socket> <some command> seems to exit silently when it's invoked in an environment which has no terminal (which is Docker's default) but works fine if I make Docker allocate a terminal. That would make sense for the -c mode, but I'd imagine that -N could theoretically work just fine when dtach is started in a "terminal-less" environment since it creates its own PTY for the command and never attaches to it. Is this just a side effect of how dtach currently handles terminals, or is there a fundamental limitation in the Linux APIs that would prevent dtach from functioning correctly in a terminal-less environment without daemonizing?

It's an easy enough fix in my own project to just allocate a terminal, but I figured I'd mention it in case you thought it was worth looking at eventually.

Hi, I couldn't find any way to attach to a session and execute a command from a script. I tried searching for help or trying out stuff on my own, but nothing work, is there no way to do this? I found that screen has the -dm switches that serve for this purpose, so it'd be nice to have something similar.

dtach -N /tmp/d1 echo "ASD" exits silently.

Let me explain an example where this is definitely a requirement. Consider the systemd unit as below:

[Unit]
Description=systemd integration for rtorrent using dtach - starts/stops rtorrent instances on startup/shutdown
Wants=network-online.target
After=network-online.target

[Service]
Environment="TERM=rxvt-unicode-256color"
KillMode=none
ExecStartPre=/usr/bin/mkdir -p %t/dtach
ExecStart=/usr/bin/dtach -N %t/dtach/rtorrent /usr/bin/rtorrent -n -o import=%E/rtorrent/.rtorrent.rc
ExecStop=/usr/bin/killall -u %u -w -s INT /usr/bin/rtorrent
# Refer https://github.com/crigler/dtach/issues/12, Success is error code 1
SuccessExitStatus=1

[Install]
WantedBy=default.target

Now what happens when rtorrent fails to start, say to due a config error? It prints to stderr/stdout. So will almost every cli program ranging from a simple echo to something heavy like rtorrent.

If I am running in foreground, then it would be prudent to redirect stdout/stderr of the command in question, or atleast have an option to do so.

it would be nice if detach would allow for a way to figure out if a session is attached or not. screen uses the execute bit on the socket to document this: when a session is attached, it's executable, when it's not, it's not.

irssi can use that to automatically mark users as away for example.

It happens after reattaching.

I was wondering if it's possible to capture the STDOUT from dtach socket to a log file. The idea is to capture all the session into a log file that I can analyse later.

I have tried playing with socat but could not find the correct incantation. Is that even possible?