Change temporary file directory

[laur89]

I'm running tmux on a host Linux OS. Many of my scripts use the fzf --tmux flag to utilize tmux native pop-up function.
I also run many workloads in a bubblewrap sandboxes. This means in a given tmux session, e.g. one pane might be running a sandboxed shell.

Problem:
When I run a script in said sandboxed shell that uses fzf --tmux, it fails, as it cannot access the shielded temporary file from host, e.g. /tmp/fzf-temp-3028728627.code.

Possible solution:
Provide an optional environment variable to fzf that dictates which directory to use for these temporary files (would still default to /tmp), so this directory could be shared with the sandbox. We could share the entire /tmp, but that's generally not wanted.

---

Or are there other solutions how to solve this conflict?

[wmorin]

You don't need a new option: fzf already honours TMPDIR. The script file comes from os.CreateTemp("", "fzf-temp-*") (src/functions.go) and the input/output fifos from filepath.Join(os.TempDir(), ...) (src/proxy.go). On Unix, Go's os.TempDir() returns $TMPDIR and falls back to /tmp only when it's unset.

The catch is that tmux display-popup starts the popup from the tmux server, so it runs on the host. fzf passes it sh /path/to/fzf-temp-XXX and -d $PWD, and that script calls fzf by the same path it was launched with and reads/writes the fifos by absolute path. All of those paths have to resolve to the same thing on the host and inside the sandbox. So bind a host directory at an identical path and point TMPDIR at it:

mkdir -m 700 -p "$XDG_RUNTIME_DIR/fzf"   # e.g. /run/user/1000/fzf
bwrap ... \
  --bind "$XDG_RUNTIME_DIR/fzf" "$XDG_RUNTIME_DIR/fzf" \
  --setenv TMPDIR "$XDG_RUNTIME_DIR/fzf" \
  ...

You can also set TMPDIR only for fzf with TMPDIR=... fzf --tmux. The generated script exports the caller's whole environment, TMPDIR included, so the popup side ends up with the same value.

Two side effects. The script runs fzf as you invoked it (argv[0]), with your sandbox PATH and cwd, so that fzf and the cwd have to exist at the same paths on the host too. And the popup fzf runs outside the sandbox, so --preview, execute() and friends run on the host as well.

https://github.com/junegunn/fzf/blob/master/src/proxy.go

Does your sandbox bind the same fzf binary and working dir at host paths, or are those different too?

[kk376]

$TMPDIR already does this. Since fzf is in Go, os.CreateTemp and os.TempDir respect it out of the box.

You can point it to a dedicated folder and bind-mount just that into the sandbox:

export TMPDIR="/run/user/$UID/fzf-tmp"
mkdir -p "$TMPDIR"

# Add to your bwrap args:
--bind "$TMPDIR" "$TMPDIR" --setenv TMPDIR "$TMPDIR"