config: make temporary directory user-configurable

See #5591

docs/content/docs.md

@@ -1554,6 +1554,22 @@ If using `--syslog` this sets the syslog facility (e.g. `KERN`, `USER`).
 See `man syslog` for a list of possible facilities.  The default
 facility is `DAEMON`.
 
+### --temp-dir=DIR ###
+
+Specify the directory rclone will use for temporary files, to override
+the default. Make sure the directory exists and have accessible permissions.
+
+By default the operating system's temp directory will be used:
+- On Unix systems, `$TMPDIR` if non-empty, else `/tmp`.
+- On Windows, the first non-empty value from `%TMP%`, `%TEMP%`, `%USERPROFILE%`, or the Windows directory.
+
+When overriding the default with this option, the specified path will be
+set as value of environment variable `TMPDIR` on Unix systems
+and `TMP` and `TEMP` on Windows.
+
+You can use the [config paths](/commands/rclone_config_paths/)
+command to see the current value.
+
 ### --tpslimit float ###
 
 Limit transactions per second to this number. Default is 0 which is

docs/content/flags.md

@@ -21,6 +21,7 @@ These flags are available for every command.
       --bwlimit BwTimetable                  Bandwidth limit in KiB/s, or use suffix B|K|M|G|T|P or a full timetable.
       --bwlimit-file BwTimetable             Bandwidth limit per file in KiB/s, or use suffix B|K|M|G|T|P or a full timetable.
       --ca-cert string                       CA certificate used to verify servers
+      --temp-dir string                      Directory rclone will use for temporary files. (default "$TMPDIR")
       --cache-dir string                     Directory rclone will use for caching. (default "$HOME/.cache/rclone")
       --check-first                          Do all the checks before starting transfers.
       --checkers int                         Number of checkers to run in parallel. (default 8)