101 lines
3.5 KiB
Markdown
101 lines
3.5 KiB
Markdown
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reptyr - A tool for "re-ptying" programs.
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=========================================
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reptyr is a utility for taking an existing running program and
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attaching it to a new terminal. Started a long-running process over
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ssh, but have to leave and don't want to interrupt it? Just start a
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screen, use reptyr to grab it, and then kill the ssh session and head
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on home.
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USAGE
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-----
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reptyr PID
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"reptyr PID" will grab the process with id PID and attach it to your
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current terminal.
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After attaching, the process will take input from and write output to
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the new terminal, including ^C and ^Z. (Unfortunately, if you
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background it, you will still have to run "bg" or "fg" in the old
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terminal. This is likely impossible to fix in a reasonable way without
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patching your shell.)
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"But wait, isn't this just screenify?"
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--------------------------------------
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There's a shell script called "screenify" that's been going around the
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internet for nigh on 10 years now that uses gdb to (supposedly)
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accomplish the same thing. The difference is that reptyr works much,
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much, better.
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If you attach a "less" using screenify, it will still take input from
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the old terminal. If you attach an ncurses program using screenify,
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and resize the window, your program won't notice. If you attach a
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process with screenify, ^C in the new terminal won't work.
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reptyr fixes all of these problems, and is the only such tool I know
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of that does so. See below for some more details on how it
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accomplishes this.
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PORTABILITY
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-----------
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reptyr is Linux-only. It uses ptrace to attach to the target and control it at
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the syscall level, so it is highly dependent on Linux's particular syscall API,
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syscalls, and terminal ioctl()s. A port to Solaris or BSD may be technically
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feasible, but would probably require significant re-architecting to abstract out
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the platform-specific bits.
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reptyr works on i386, x86_64, and ARM. Ports to other architectures should be
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straightforward, and should in most cases be as simple as adding an arch/ARCH.h
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file and adding a clause to the ifdef ladder in ptrace.c.
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ptrace_scope on Ubuntu Maverick and up
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--------------------------------------
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`reptyr` depends on the `ptrace` system call to attach to the remote program. On
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Ubuntu Maverick and higher, this ability is disabled by default for security
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reasons. You can enable it temporarily by doing
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# echo 0 > /proc/sys/kernel/yama/ptrace_scope
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as root, or permanently by editing the file /etc/sysctl.d/10-ptrace.conf, which
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also contains more information about exactly what this setting accomplishes.
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reptyr -l
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---------
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As a bonus feature, if you run "reptyr -l", reptyr will create a new
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pseudo-terminal pair with nothing attached to the slave end, and print
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its name out.
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If you are debugging a program in gdb, you can pass that name to "set
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inferior-pty". Because there is no existing program listening to that
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tty, this will work much better than passing an existing shell's
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terminal.
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How does it work?
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-----------------
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The main thing that reptyr does that no one else does is that it
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actually changes the controlling terminal of the process you are
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attaching. I plan on writing up more about just how this works soon,
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but for now, the source is only about 1000 lines if you're curious :)
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PRONUNCIATION
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-------------
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I pronounce it like "repeater", but since that's easily ambiguous,
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"re-P-T-Y-er" is also acceptable.
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CREDITS
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-------
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reptyr was written by Nelson Elhage <nelhage@nelhage.com>. Contact him
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with any questions or bug reports.
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URL
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---
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[http://github.com/nelhage/reptyr]()
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