try

"Do, or do not. There is no try."

We're setting out to change that: try cmd and commit---or not.

Description

try lets you run a command and inspect its effects before changing your live system. try uses Linux's namespaces (via unshare) and the overlayfs union filesystem.

Please note that try is a prototype and not a full sandbox, and should not be used to execute commands that you don't already trust on your system, (i.e. network calls are all allowed)

Getting Started

Dependencies

try relies on the following Debian packages

util-linux (for standard Linux utilities, findmnt)
attr (for getfattr)
pandoc and autoconf (if working from a GitHub clone)

In cases where overlayfs doesn't work on nested mounts, you will need either mergerfs or unionfs. try should be able to autodetect them, but you can specify the path to mergerfs or unionfs with -U (e.g. try -U ~/.local/bin/unionfs)

To run try's test suite (scripts/run_tests.sh), you will need:

bash
expect
curl

try has been tested on the following distributions:

Ubuntu 20.04 LTS or later
Debian 12
Fedora 38
Centos 9 Stream 5.14.0-325.el9
Arch 6.1.33-1-lts
Alpine 6.1.34-1-lts
Rocky 9 5.14.0-284.11.1.el9_2
SteamOS 3.4.8 5.13.0-valve36-1-neptune

Note that try will only work on Linux 5.11 or higher for overlayfs to work in a user namespace.

Installing

There are three ways to install try:

The quick and janky way: grab the script. You only need the try script. Put it in your PATH and you're ready to go. You won't have documentation or utility support, but it should work as is.
By cloning the repository. Run the following:

$ git clone https://github.com/binpash/try.git
$ autoconf && ./configure && make && sudo make install

You should now have a fully featured try, including the support utilities (which should help try run faster) and manpage. Run make test to confirm that everything works.

By using a source distribution. Download try-XXX.tgz from the release page. You can get the latest prerelease by downloading try-latest.tgz. You can then install similarly to the above:

$ git clone https://github.com/binpash/try.git
$ ./configure && make && sudo make install

The repository and source distribution are slightly different: the repository does not include the configure script (generated by autoconf) or the manpage (generated by pandoc), but the source distribution does.

Arch Linux

try is present in AUR, you can install it with your preferred AUR helper:

yay -S try

or manually:

git clone https://aur.archlinux.org/try.git
cd try
makepkg -sic

Example Usage

try is a higher-order command, like xargs, exec, nohup, or find. For example, to install a package via pip3, you can invoke try as follows:

$ try pip3 install libdash
... # output continued below

By default, try will ask you to commit the changes made at the end of its execution.

...
Defaulting to user installation because normal site-packages is not writeable
Collecting libdash
  Downloading libdash-0.3.1-cp310-cp310-manylinux_2_17_x86_64.manylinux2014_x86_64.whl (254 kB)
     ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 254.6/254.6 KB 2.1 MB/s eta 0:00:00
Installing collected packages: libdash
Successfully installed libdash-0.3.1
WARNING: Running pip as the 'root' user can result in broken permissions and conflicting behaviour with the system package manager. It is recommended to use a virtual environment instead: https://pip.pypa.io/warnings/venv

Changes detected in the following files:

/tmp/tmp.zHCkY9jtIT/upperdir/home/gliargovas/.local/lib/python3.10/site-packages/libdash/ast.py (modified/added)
/tmp/tmp.zHCkY9jtIT/upperdir/home/gliargovas/.local/lib/python3.10/site-packages/libdash/_dash.py (modified/added)
/tmp/tmp.zHCkY9jtIT/upperdir/home/gliargovas/.local/lib/python3.10/site-packages/libdash/__init__.py (modified/added)
/tmp/tmp.zHCkY9jtIT/upperdir/home/gliargovas/.local/lib/python3.10/site-packages/libdash/__pycache__/printer.cpython-310.pyc (modified/added)
/tmp/tmp.zHCkY9jtIT/upperdir/home/gliargovas/.local/lib/python3.10/site-packages/libdash/__pycache__/ast.cpython-310.pyc (modified/added)
<snip>

Commit these changes? [y/N] y

Sometimes, you might want to pre-execute a command and commit its result at a later time. Running try -n will print the overlay directory on STDOUT without committing the result.

$ try -n "curl https://sh.rustup.rs | sh"
/tmp/tmp.uCThKq7LBK

Alternatively, you can specify your own existing overlay directory using the -D [dir] flag:

$ mkdir rustup-sandbox
$ try -D rustup-sandbox "curl https://sh.rustup.rs | sh"
$ ls rustup-sandbox
temproot  upperdir  workdir

As you can see from the output above, try has created an overlay environment in the rustup-sandbox directory.

Manually inspecting upperdir reveals the changes to the files made inside the overlay during the execution of the previous command with try:

~/try/rustup-sandbox/upperdir$ du -hs .
1.2G    .

You can inspect the changes made inside a given overlay directory using try:

$ try summary rustup-sandbox/ | head

Changes detected in the following files:

rustup-sandbox//upperdir/home/ubuntu/.profile (modified/added)
rustup-sandbox//upperdir/home/ubuntu/.bashrc (modified/added)
rustup-sandbox//upperdir/home/ubuntu/.rustup/update-hashes/stable-x86_64-unknown-linux-gnu (modified/added)
rustup-sandbox//upperdir/home/ubuntu/.rustup/settings.toml (modified/added)
rustup-sandbox//upperdir/home/ubuntu/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/libstd-8389830094602f5a.so (modified/added)
rustup-sandbox//upperdir/home/ubuntu/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/etc/lldb_commands (modified/added)
rustup-sandbox//upperdir/home/ubuntu/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/etc/gdb_lookup.py (modified/added)

You can also choose to commit the overlay directory contents:

$ try commit rustup-sandbox

You can also run try explore to open your current shell in try, or /try explore /tmp/tmp.X6OQb5tJwr to explore an existing sandbox.

To specify multiple lower directories for overlay (by merging them together), you can use the -L (implies -n) flag followed by a colon-separated list of directories. The directories on the left have higher precedence and can overwrite the directories on the right:

$ try -D /tmp/sandbox1 "echo 'File 1 Contents - sandbox1' > file1.txt"
$ try -D /tmp/sandbox2 "echo 'File 2 Contents - sandbox2' > file2.txt"
$ try -D /tmp/sandbox3 "echo 'File 2 Contents - sandbox3' > file2.txt"

# Now use the -L flag to merge both sandbox directories together, with sandbox3 having precedence over sandbox2
$ try -L "/tmp/sandbox3:/tmp/sandbox2:/tmp/sandbox1" "cat file1.txt file2.txt"
File 1 Contents - sandbox1
File 2 Contents - sandbox3

In this example, try will merge /sandbox1, /sandbox2 and /sandbox3 together before mounting the overlay. This way, you can combine the contents of multiple try sandboxes.

Known Issues

Any command that interacts with other users/groups will fail since only the current user's UID/GID are mapped. However, the future branch has support for uid/mapping; please refer to the that branch's readme for installation instructions for the uid/gidmapper (root access is required for installation).

Shell quoting may be unintuitive, you may expect try bash -c "echo a" to work, however, try will actually execute bash -c echo a, which will not result in a being printed. We are currently not planning on resolving this behavior.

Please also report any issue you run into while using the future branch!

Version History

v0.2.0 - 2023-07-24
- Refactor tests.
- Improved linting.
- Hide try-internal variables from scripts.
- Style guide.
- Testing in Vagrant.
- Support nested mounts.
- Resolve issues with userxattr.
- Better support for unionfs.
- Use /bin/sh, not /bin/bash.
- -i flag to ignore paths.
- Interactive improvements.
v0.1.0 - 2023-06-25
- Initial release.

License

This project is licensed under the MIT License - see LICENSE for details.

wrongbyte/try

try