archive and download logs (feature)

* docs - initial
* part three, prev. commit: c5891ae

Signed-off-by: Alex Aizman <[email protected]>

docs/cli.md

@@ -103,6 +103,7 @@ Following is a brief summary (that's non-exhaustive and slightly outdated):
 | [`ais object`](/docs/cli/object.md) | PUT and GET (write and read), APPEND, archive, concat, list (buckets, objects), move, evict, promote, ... |
 | [`ais search`](/docs/cli/search.md) | Search `ais` commands. |
 | [`ais show`](/docs/cli/show.md) | Monitor anything and everything: performance (all aspects), buckets, jobs, remote clusters, and more. |
+| [`ais log`](/docs/cli/log.md) | Download ais nodes' logs or view the logs in real time. |
 | [`ais storage`](/docs/cli/storage.md) | Show capacity usage on a per bucket basis (num objects and sizes), attach/detach mountpaths (disks). |
 {: .nobreak}
 

docs/cli/log.md

@@ -0,0 +1,68 @@
+---
+layout: post
+title: LOG
+permalink: /docs/cli/log
+redirect_from:
+ - /cli/log.md/
+ - /docs/cli/log.md/
+---
+
+# Table of Contents
+- [Download log or all logs (including history)](#ais-log-get-command)
+- [View current log](#ais-log-show-command)
+
+# `ais log get` command
+
+```console
+$ ais log get --help
+NAME:
+   ais log get - download log (or all logs including history) from selected node or all nodes in the cluster, e.g.:
+               - 'ais log get NODE_ID /tmp' - download the specified node's current log; save the result to the specified directory;
+               - 'ais log get NODE_ID /tmp/out --refresh 10' - download the current log as /tmp/out
+                  keep updating (ie., appending) the latter every 10s;
+               - 'ais log get cluster /tmp' - download TAR.GZ archived logs from _all_ nodes in the cluster
+                  ('cluster' implies '--all') and save the result to the specified destination;
+               - 'ais log get NODE_ID --all' - download the node's TAR.GZ log archive
+               - 'ais log get NODE_ID --all --severity e' - TAR.GZ archive of (only) logged errors and warnings
+
+USAGE:
+   ais log get [command options] NODE_ID [OUT_FILE|OUT_DIR|-]
+
+OPTIONS:
+   --refresh value   interval for continuous monitoring;
+                     valid time units: ns, us (or µs), ms, s (default), m, h
+   --count value     used together with '--refresh' to limit the number of generated reports, e.g.:
+                      '--refresh 10 --count 5' - run 5 times with 10s interval (default: 0)
+   --severity value  log severity is either 'info' (default) or 'error', whereby error logs contain both errors and warnings, e.g.:
+                     - 'ais show log NODE_ID'
+                     - 'ais log show NODE_ID --severity i' - same as above
+                     - 'ais show log NODE_ID --severity error' - errors and warnings only
+                     - 'ais show log NODE_ID --severity w' - same as above
+   --yes, -y         assume 'yes' to all questions
+   --all             download all logs
+   --help, -h        show help
+```
+
+# `ais log show` command
+
+```console
+$ ais log show --help
+NAME:
+   ais log show - for a given node: show its current log (use '--refresh' to update, '--help' for details)
+
+USAGE:
+   ais log show [command options] NODE_ID
+
+OPTIONS:
+   --refresh value    interval for continuous monitoring;
+                      valid time units: ns, us (or µs), ms, s (default), m, h
+   --count value      used together with '--refresh' to limit the number of generated reports, e.g.:
+                       '--refresh 10 --count 5' - run 5 times with 10s interval (default: 0)
+   --severity value   log severity is either 'info' (default) or 'error', whereby error logs contain both errors and warnings, e.g.:
+                      - 'ais show log NODE_ID'
+                      - 'ais log show NODE_ID --severity i' - same as above
+                      - 'ais show log NODE_ID --severity error' - errors and warnings only
+                      - 'ais show log NODE_ID --severity w' - same as above
+   --log-flush value  can be used in combination with '--refresh' to override configured 'log.flush_time'
+   --help, -h         show help
+```