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--cidfile fails if file exists even if empty

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#5,954 4 comments 0 reactions 0 assignees View on GitHub

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
68/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Active
Tech stack
docker, go
Domain
cli

Research direction

Start at the docker run --cidfile handling and reproduce the reported case with a path created by mktemp. Done means an existing empty cidfile no longer causes failure, while a cidfile containing a PID retains the intended failure behavior; add or update coverage for these cases where the CLI tests for this entry point are located.

Written by the indexing model from the issue text.

Description

kind/enhancement status/0-triage
Description

The best practice when creating a temporary file is not only to generate a filename of a file that does not already exist, but also to create/open the file with O_EXCL, to avoid TOCTOU, typically that's what mkstemp(3) does.
Unfortunately, docker-run's --cidfile prevents from passing it a safe temporary file, because docker-run will fail if the given file merely exists.

Reproduce
t=$(mktemp)
docker run --rm --cidfile=$t debian
Expected behavior

docker-run should fail only if the file given as --cidfile contains a PID (even better, check if the PID is alive by using kill(the_pid, 0) which is designed for that)

docker version
Client:
 Version:           20.10.24+dfsg1
 API version:       1.41
 Go version:        go1.19.8
 Git commit:        297e128
 Built:             Sat Oct 12 15:19:49 2024
 OS/Arch:           linux/amd64
 Context:           default
 Experimental:      true

Server:
 Engine:
  Version:          20.10.5+dfsg1
  API version:      1.41 (minimum version 1.12)
  Go version:       go1.15.15
  Git commit:       363e9a8
  Built:            Mon May 30 18:34:49 2022
  OS/Arch:          linux/amd64
  Experimental:     false
 containerd:
  Version:          1.6.20~ds1
  GitCommit:        1.6.20~ds1-1+deb12u1
 runc:
  Version:          1.1.5+ds1
  GitCommit:        1.1.5+ds1-1+deb12u1
 docker-init:
  Version:          0.19.0
  GitCommit:
docker info
too much identifying info
Additional Info

No response

Dominant language
Go
Stars
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Forks
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Avg merge
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Merged PRs (30d)
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