Incomplete uninstallations leave the system in a tricky state #34

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opened 2024-11-12 14:59:30 +00:00 by lheckemann · 1 comment

lheckemann commented

2024-11-12 14:59:30 +00:00

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To reproduce (on macOS):

cd /nix
./nix-installer uninstall

The uninstallation will fail because /nix is still in use (as the working directory of the shell from which the uninstaller was invoked) and can't be unmounted/deleted.

Attempting to uninstall again will fail more spectacularly because some of the steps will have been reverted already.

To reproduce (on macOS): - cd `/nix` - `./nix-installer uninstall` The uninstallation will fail because `/nix` is still in use (as the working directory of the shell from which the uninstaller was invoked) and can't be unmounted/deleted. Attempting to uninstall again will fail more spectacularly because some of the steps will have been reverted already.

ktemkin self-assigned this

2025-09-21 16:42:21 +00:00

kfearsoff commented

2025-12-10 13:09:52 +00:00

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I'm puzzled by why this happens, as there's a very clear attempt in the uninstall command to mitigate this:

Preview has been truncated

         if let Ok(current_dir) = std::env::current_dir() {
             let mut components = current_dir.components();
             let should_be_root = components.next();
             let maybe_nix = components.next();
             if should_be_root == Some(std::path::Component::RootDir)
                 && maybe_nix == Some(std::path::Component::Normal(std::ffi::OsStr::new("nix")))
             {
                 tracing::debug!("Changing current directory to be outside of `/nix`");
                 std::env::set_current_dir("/").wrap_err("Uninstall process was run from `/nix` folder, but could not change directory away from `/nix`, please change the current directory and try again.")?;
             }
         }
         // During install, `nix-installer` will store a copy of itself in `/nix/nix-installer`
         // If the user opted to run that particular copy of `nix-installer` to do this uninstall,
         // well, we have a problem, since the binary would delete itself.
         // Instead, detect if we're in that location, if so, move the binary and `execv` it.
         if let Ok(current_exe) = std::env::current_exe() {
             if current_exe.as_path() == Path::new("/nix/nix-installer") {
                 tracing::debug!(
                     "Detected uninstall from `/nix/nix-installer`, moving executable and re-executing"
                 );
                 let temp = std::env::temp_dir();
                 let random_trailer: String = {
                     const CHARSET: &[u8] = b"ABCDEFGHIJKLMNOPQRSTUVWXYZ\
                                         abcdefghijklmnopqrstuvwxyz\
                                             0123456789";
                     const PASSWORD_LEN: usize = 16;
                     let mut rng = rand::thread_rng();
                     (0..PASSWORD_LEN)
                         .map(|_| {
                             let idx = rng.gen_range(0..CHARSET.len());
                             CHARSET[idx] as char
                         })
                         .collect()
                 };
                 let temp_exe = temp.join(&format!("nix-installer-{random_trailer}"));
                 tokio::fs::copy(&current_exe, &temp_exe)
                     .await
                     .wrap_err("Copying nix-installer to tempdir")?;
                 let args = std::env::args();
                 let mut arg_vec_cstring = vec![];
                 for arg in args {
                     arg_vec_cstring.push(CString::new(arg).wrap_err("Making arg into C string")?);
                 }
                 let temp_exe_cstring = CString::new(temp_exe.to_string_lossy().into_owned())
                     .wrap_err("Making C string of executable path")?;
                 tracing::trace!("Execv'ing `{temp_exe_cstring:?} {arg_vec_cstring:?}`");
                 nix::unistd::execv(&temp_exe_cstring, &arg_vec_cstring)

Does it fail despite that? Is it some kind of issue with std::env::set_current_dir?

I'm puzzled by why this happens, as there's a very clear attempt in the `uninstall` command to mitigate this: https://git.lix.systems/lix-project/lix-installer/src/commit/81a5d136aaf6b81adc044171f1eb118220d99b9e/src/cli/subcommand/uninstall.rs#L57-L109 Does it fail despite that? Is it some kind of issue with `std::env::set_current_dir`?