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Merge pull request #17683 from TomSweeneyRedHat/dev/tsweeney/lockdoc 

[CI:DOCS] Add image not found info to troubleshooting
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@ -1344,3 +1344,45 @@ $ podman run --rm \
Replace `/bin/cat /proc/self/uid_map` with
`/bin/cat /proc/self/gid_map` to show the GID mapping.
### 40) Podman fails to find expected image with "error locating pulled image", "image not known"
When trying to do a Podman command that pulls an image from local storage or a remote repository,
an error is raised saying "image not known" or "error locating pulled image". Even though the image
had been verified before the Podman command was invoked.
#### Symptom
After verifying that an image is in place either locally or on a remote repository, a Podman command
referencing that image will fail in a manner like:
```
# ls Containerfile
FROM registry.access.redhat.com/ubi8-minimal:latest
MAINTAINER Podman Community
USER root
# podman build .
STEP 1/2: FROM registry.access.redhat.com/ubi8-minimal
Trying to pull registry.access.redhat.com/ubi8-minimal:latest...
Getting image source signatures
Checking if image destination supports signatures
Copying blob a6577091999b done
Copying config abb1ba1bce done
Writing manifest to image destination
Storing signatures
Error: error creating build container: error locating pulled image "registry.access.redhat.com/ubi8-minimal:latest" name in containers storage: registry.access.redhat.com/ubi8-minimal:latest: image not known
```
#### Solution
The general cause for this is a timing issue. To make Podman commands as
efficient as possible, read and write locks are only established for critical
sections within the code. When pulling an image from a repository, a copy of
that image is first written to local storage using a write lock. This lock is
released before the image is then acquired/read. If another process does a
harmful command such as `podman system prune --all` or `podman system reset`
or `podman rmi --all`, between the time the image is written and before the
first process can acquire it, this type of `image not known` error can arise.
The maintainers of Podman have considered heavier-duty locks to close this
timing window. However, the slowdown that all Podman commands would encounter
was not considered worth the cost of completely closing this small timing window.