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ssrv

ssrv is a versatile networking tool designed to enable efficient command execution across different systems. It operates as both a server and a client, facilitating remote shell access and command execution. With a focus on flexibility and control, users can specify environment variables, choose whether to allocate a pseudo-terminal, and define the socket for communication.

Key features include:

  • Multiplexed Connections: Allows handling multiple clients simultaneously, ensuring robustness and scalability.
  • Customizable Environment Variables: Users can pass a comma-separated list of environment variables to the server side process, providing fine-grained control over the session environment. And with the ability to specify exceptions when passing/unsetting all env vars: -env all-:MY_VAR,MY_VAR1 -uenv all-:MY_VAR2,MY_VAR3
  • Pseudo-Terminal Allocation: Offers options to force or avoid allocating a pseudo-terminal, accommodating various command behaviors and client requirements.
  • Dynamically Resizing Pseudo-Terminal: Dynamically changing the size of the pseudo-terminal along with the size of the window.
  • Command Execution: When no command is passed, the default behavior is to spawn a shell on the server side, offering full shell functionality to the client. The remote command exit code is also returned to the client.
  • Shims for the server side binaries: If there's a process that you always want to execute on the server side system, you can create a symlink to it somewhere in your $PATH and it'll always be executed through ssrv.
  • Stdin Pipe: Sends data to the command's standard input using a pipe.
  • Separate Stdout and Stderr: The client receives stdout and stderr in a separate channels.
  • Port Forwarding: Forward remote TCP and UDP ports to local ports.
  • BG Control: Client background processes control (without suspending tty output). And sending syscall.Signal's to client pids on server side if running without allocation pty.
  • Exit Code Forwarding: Return the exit code to the client.
  • Setting CWD Path: Changing the current working directory of the process/command.

ssrv is ideal for system administrators and developers who require a solution for executing commands remotely or locally with listening on unix sockets. By default, the server and the client communicate via an abstract unix socket @ssrv. Its configurability and support for multiple concurrent sessions make it suitable for complex network operations and management tasks.

To get started:

  • Install the latest revision
go install github.com/VHSgunzo/ssrv@latest
  • Or take an already precompiled binary file from the releases

Usage:

┌──[user@linux]─[~] - Server:
└──╼ $ ssrv -srv [-sock tcp:1337] [-env all]
┌──[user@linux]─[~] - Client:
└──╼ $ ssrv [options] [ COMMAND [ arguments... ] ]

If COMMAND is not passed, spawn a $SHELL on the server side.

Accepted options:
    -L string
        Comma separated list of remote port forwarding to local port <local_port:remote_port>
    -N  Don't execute commands. (Use with port forwarding)
    -cpids-dir string
        A directory on the server side for storing a list of client PIDs. (default "/tmp/ssrv$EUID")
    -cwd string
        Change the current working directory of the process/command.
    -env string
        Comma separated list of environment variables to pass to the server side process. (default "TERM")
    -no-pty
        Do not allocate a pseudo-terminal for the server side process
    -nosep-cpids
        Don't create a separate dir for the server socket to store the list of client PIDs.
    -pid-file string
        The file for storing the server's PID.
    -pty
        Force allocate a pseudo-terminal for the server side process
    -srv
        Run as server
    -sock string
        Socket address listen/connect (unix,tcp,tcp4,tcp6) (default "unix:@ssrv")
    -uenv string
        Comma separated list of environment variables for unset on the server side process.
    -v
        Show this program's version

--

Environment variables:
    SSRV_PTY=1                      Same as -pty argument
    SSRV_NO_PTY=1                   Same as -no-pty argument
    SSRV_ENV="MY_VAR,MY_VAR1"       Same as -env argument
    SSRV_UENV="MY_VAR,MY_VAR1"      Same as -uenv argument
    SSRV_SOCK="tcp:1337"            Same as -sock argument
    SSRV_CPIDS_DIR=/path/dir        Same as -cpids-dir argument
    SSRV_NOSEP_CPIDS=1              Same as -nosep-cpids argument
    SSRV_PID_FILE=/path/ssrv.pid    Same as -pid-file argument
    SSRV_CWD=/path/dir              Same as -cwd argument
    SSRV_NO_EXEC=1                  Same as -N argument
    SSRV_LPORTFW="22:22,53:53/udp"  Same as -L argument
    SHELL="/bin/bash"               Assigns a default shell (on the server side)

--

If none of the pty arguments are passed in the client, a pseudo-terminal is allocated by default, unless it is
known that the command behaves incorrectly when attached to the pty or the client is not running in the terminal

Example of creating a shim for the flatpak command:

# Inside your container:

$ flatpak --version
zsh: command not found: flatpak

# Have ssrv handle any flatpak command
$ ln -s /usr/local/bin/ssrv /usr/local/bin/flatpak

# Now flatpak will always be executed on the server side
$ flatpak --version
Flatpak 1.12.7

Note: you will want to store the symlink in a location visible only to the container, to avoid an infinite loop. If you are using toolbox/distrobox, this means anywhere outside your home directory. I recommend /usr/local/bin.

Example of file transfer to server:

# one file:
ssrv sh -c 'cat>/server/path/some_file.tar.zst' </client/path/some_file.tar.zst

# directory with zstd compression:
tar -I 'zstd -T0 -1' -c /client/path/some_dir|ssrv tar --zstd -xf - -C /server/path/some_dir

Example of file transfer from server:

# one file:
ssrv cat /server/path/some_file.tar.zst > /client/path/some_file.tar.zst

# directory with zstd compression:
ssrv tar -I 'zstd -T0 -1' -c /server/path/some_dir|tar --zstd -xf - -C /client/path/some_dir
# or dir to archive:
ssrv tar -I 'zstd -T0 -1' -c /server/path/some_dir > /client/path/some_dir.tar.zst