03 Feb 2011
reptyr - Reparent a running program to a new terminal
reptyr -l|-L [COMMAND [ARGS]]
reptyr is a utility for taking an existing running program and attaching it to a new terminal. Started a long-running process over ssh, but have to leave and don’t want to interrupt it? Just start a screen, use reptyr to grab it, and then kill the ssh session and head on home.
reptyr works by attaching to the target program using ptrace(2), redirecting relevant file descriptors, and changing the program’s controlling terminal (See tty(4)) It is this last detail that makes reptyr work much better than alternatives such as retty(1).
After attaching a program, the program will appear to be either backgrounded or suspended to the shell it was launched from (depending on the shell). For maximal safety you can run
in the old shell to remove the association with the program, but reptyr will attempt to ensure that the target program remains running even if you close the shell without doing so.
|Use an alternate mode of attaching, "TTY-stealing". In this mode, reptyr will not ptrace(2) the target process, but will attempt to discover the terminal emulator for that process’ pty, and steal the master end of the pty. This mode is more reliable and flexible in many circumstances (for instance, it can attach all processes on a tty, rather than just a single process). However, as a downside, children of sshd(8) cannot be attached via -T unless reptyr is run as root. See for more information about tty-stealing.|
-l, -L [COMMAND [ARGS]]
|Instead of attaching to a new process, create a new pty pair, proxy the master end to the current terminal, and then print the name of the slave pty. This can be passed to e.g. gdb's set inferior-tty option.
If an optional COMMAND and ARGS are passed in conjunction with -l, that command will be executed as a child of reptyr with the REPTYR_PTY environment variable set to the name of the slave pty. If -L is used instead of -l, then fds 0-2 of the child will also be redirected to point to the slave, and the child will be run in a fresh session with the slave as its controlling terminal.
By default, reptyr will move any file descriptors in the target that were connected to the target’s controlling terminal to point to the new terminal. The -s option will cause reptyr to unconditionally attach file descriptors 0, 1, and 2 in the target, even if the target has no controlling terminal or they are not connected to a terminal.
|Print the version of reptyr and exit.|
|Print a usage message and exit.|
|Print verbose debug output while running.|
reptyr depends on the ptrace(2) system call to attach to the remote program. On Ubuntu Maverick and higher, this ability is disabled by default for security reasons. You can enable it temporarily by doing
|# echo 0 > /proc/sys/kernel/yama/ptrace_scope|
When attaching to some curses programs, they will not redraw the screen right away, and a ^L or similar will be needed to force a redraw.
Similarly, after attaching to certain programs, the old terminal will be left in an odd state, and a clear or even reset may be required before the old terminal is usable again.
Attaching to rtorrent (and probably some other apps) doesn’t work right (rtorrent stops accepting input) (The problem is that rtorrent is using epoll to poll stdin, and we don’t update the internal reference that the epoll fd has to the old tty).
Attaching to a process with children doesn’t work right. This should be possible to fix -- I just need to ptrace each child individually and do the same games to it.
Attaching a less(1) process doesn’t work if you have a .lessfilter file, as less leaves around a zombie child in this case. This could be worked around.
Bugs should be reported to the author (see below) or via the issue tracker on GitHub.
reptyr was written by Nelson Elhage <nelhage>.