Add --filter to podman system prune

Also document the allowable filters in podman system prune, podman image prune
and podman container prune.

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/docs/source/markdown/podman-system-prune.1.md b/docs/source/markdown/podman-system-prune.1.md
index 431a11267..791503a2c 100644
--- a/docs/source/markdown/podman-system-prune.1.md
+++ b/docs/source/markdown/podman-system-prune.1.md
@@ -18,6 +18,21 @@ By default, volumes are not removed to prevent important data from being deleted
 
 Recursively remove all unused pod, container, image and volume data (Maximum 50 iterations.)
 
+#### **--filter**=*filters*
+
+Provide filter values.
+
+The --filter flag format is of “key=value”. If there is more than one filter, then pass multiple flags (e.g., --filter "foo=bar" --filter "bif=baz")
+
+Supported filters:
+
+- `until` (_timestamp_) - only remove containers and images created before given timestamp
+- `label` (label=_key_, label=_key=value_, label!=_key_, or label!=_key=value_) - only remove containers and images, with (or without, in case label!=... is used) the specified labels.
+
+The until filter can be Unix timestamps, date formatted timestamps, or Go duration strings (e.g. 10m, 1h30m) computed relative to the machine’s time.
+
+The label filter accepts two formats. One is the label=... (label=_key_ or label=_key=value_), which removes containers and images with the specified labels. The other format is the label!=... (label!=_key_ or label!=_key=value_), which removes containers and images without the specified labels.
+
 #### **--force**, **-f**
 
 Do not prompt for confirmation
@@ -35,3 +50,4 @@ podman(1), podman-image-prune(1), podman-container-prune(1), podman-pod-prune(1)
 
 ## HISTORY
 February 2019, Originally compiled by Dan Walsh (dwalsh at redhat dot com)
+December 2020, converted filter information from docs.docker.com documentation by Dan Walsh (dwalsh at redhat dot com)