nix-shell /tmp/ directories deleted while still in use

[samuela]

Issue description

I occasionally encounter errors such as

[skainswo@bitbop-proxy-arm:~/dev/bitbop/cherami]$ cargo build                                                                                               
   Compiling libc v0.2.152                                                                                                                                  
   Compiling autocfg v1.1.0                                                                                                                                 
error: couldn't create a temp dir: No such file or directory (os error 2) at path "/tmp/nix-shell.s7uxvf/rustcoG5wgG"                                       
                                                                                                                                                            
error: could not compile `libc` (build script) due to previous error                                                                                        
warning: build failed, waiting for other jobs to finish...                                                                                                  
error: couldn't create a temp dir: No such file or directory (os error 2) at path "/tmp/nix-shell.s7uxvf/rustcuBk6VG"                                       
                                                                                                                                                            
error: could not compile `autocfg` (lib) due to previous error                                                                                              

in nix-shell sessions that have been open for a while.

Steps to reproduce

Open a nix-shell and leave it running for a few days. Then attempt to build some rust code.

Technical details

 - system: `"aarch64-linux"`
 - host os: `Linux 6.1.75, NixOS, 23.11 (Tapir), 23.11.5541.56528ee42526`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.18.1`
 - channels(root): `"nixos-23.11"`
 - nixpkgs: `/nix/var/nix/profiles/per-user/root/channels/nixos`

[lolbinarycat]

according to this reddit comment, nixos uses systemd's defaults, which is to delete tempfiles after 10 days.

[lolbinarycat]

however, according to the comments on #96753 (and looking at my own /tmp), this file is actually ignored.

[samuela]

Shouldn't the temp directory be kept as long as it's actively in use by a shell?

[lolbinarycat]

"actively in use by a shell" isn't something that systemd-tmpfiles can quantify. the correct way to keep tempfiles from being deleted is to periodically bump their mtime.

[samuela]

the correct way to keep tempfiles from being deleted is to periodically bump their mtime

then nix-shell should do that?

[lolbinarycat]

yes, it should. i was explaining why this is the fault of nix, not systemd-tmpfiles

[samuela]

yes, it should. i was explaining why this is the fault of nix, not systemd-tmpfiles

ah gotcha, i misunderstood the implication in your prior message. thanks for clarifying!