abduco a tool for session {at,de}tach support

abduco provides session management i.e. it allows programs to be run independently from their controlling terminal. That is programs can be detached - run in the background - and then later reattached. Together with dvtm it provides a simpler and cleaner alternative to tmux or screen.

abduco+dvtm demo

abduco is in many ways very similar to dtach but is a completely independent implementation which is actively maintained, contains no legacy code, provides a few additional features, has a cleaner, more robust implementation and is distributed under the ISC license

News

Download

Either download the latest source tarball, compile and install it

./configure && make && sudo make install

or use one of the distribution provided binary packages.

Quickstart

In order to create a new session abduco requires a session name as well as an command which will be run. If no command is given the environment variable $ABDUCO_CMD is examined and if not set dvtm is executed. Therefore assuming dvtm is located somewhere in $PATH a new session named demo is created with:

$ abduco -c demo

An arbitrary application can be started as follows:

$ abduco -c session-name your-application

CTRL-\ detaches from the active session. This detach key can be changed by means of the -e command line option, -e ^q would for example set it to CTRL-q.

To get an overview of existing session run abduco without any arguments.

$ abduco
Active sessions (on host debbook)
* Thu    2015-03-12 12:05:20    demo-active
+ Thu    2015-03-12 12:04:50    demo-finished
  Thu    2015-03-12 12:03:30    demo

A leading asterisk * indicates that at least one client is connected. A leading plus + denotes that the session terminated, attaching to it will print its exit status.

A session can be reattached by using the -a command line option in combination with the session name which was used during session creation.

$ abduco -a demo

If you encounter problems with incomplete redraws or other incompatibilities it is recommended to run your applications within dvtm under abduco:

$ abduco -c demo dvtm your-application

Check out the manual page for further information and all available command line options.

Improvements over dtach

  • session list, available by executing abduco without any arguments, indicating whether clients are connected or the command has already terminated.

  • the session exit status of the command being run is always kept and reported either upon command termination or on reconnection e.g. the following works:

     $ abduco -n demo true && abduco -a demo
 abduco: demo: session terminated with exit status 0

  • read only sessions if the -r command line argument is used when attaching to a session, then all keyboard input is ignored and the client is a passive observer only.

    Note that this is not a security feature, but only a convenient way to avoid accidental keyboard input.

    If you want to make your abduco session available to another user in a read only fashion, use socat to proxy the abduco socket in a unidirectional (from the abduco server to the client, but not vice versa) way.

    Start your to be shared session, make sure only you have access to the private directory:

     $ abduco -c /tmp/abduco/private/session

    Then proxy the socket in unidirectional mode -u to a directory where the desired observers have sufficient access rights:

     $ socat -u unix-connect:/tmp/abduco/private/session unix-listen:/tmp/abduco/public/read-only &

    Now the observers can connect to the read-only side of the socket:

     $ abduco -a /tmp/abduco/public/read-only

    communication in the other direction will not be possible and keyboard input will hence be discarded.

  • better resize handling on shared sessions, resize request are only processed if they are initiated by the most recently connected, non read only client.

  • socket recreation by sending the SIGUSR1 signal to the server process. In case the unix domain socket was removed by accident it can be recreated. The simplest way to find out the server process id is to look for abduco processes which are reparented to the init process.

     $ pgrep -P 1 abduco

    After finding the correct PID the socket can be recreated with

     $ kill -USR1 $PID

    If the abduco binary itself has also been deleted, but a session is still running, use the following command to bring back the session:

     $ /proc/$PID/exe

  • improved socket permissions the session sockets are by default either stored in $HOME/.abduco or /tmp/abduco/$USER in both cases it is made sure that only the owner has access to the respective directory.

Development

You can always fetch the current code base from the git repository located at Github or Sourcehut.

If you have comments, suggestions, ideas, a bug report, a patch or something else related to abduco then write to the suckless developer mailing list or contact me directly.

Debugging

The protocol content exchanged between client and server can be dumped to temporary files as follows:

$ make debug
$ ./abduco -n debug [command-to-debug] 2> server-log
$ ./abduco -a debug 2> client-log

If you want to run client and server with one command (e.g. using the -c option) then within gdb the option set follow-fork-mode {child,parent} might be useful. Similarly to get a syscall trace strace -o abduco -ff [abduco-cmd] proved to be handy.

License

abduco is licensed under the ISC license