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)

fs/config/config.go

@@ -712,3 +712,32 @@ func makeCacheDir() (dir string) {
 	}
 	return filepath.Join(dir, "rclone")
 }
+
+// SetTempDir sets new default directory to use for temporary files.
+//
+// Assuming golang's os.TempDir is used to get the directory:
+// "On Unix systems, it returns $TMPDIR if non-empty, else /tmp. On Windows,
+// it uses GetTempPath, returning the first non-empty value from %TMP%, %TEMP%,
+// %USERPROFILE%, or the Windows directory."
+//
+// To override the default we therefore set environment variable TMPDIR
+// on Unix systems, and both TMP and TEMP on Windows (they are almost exclusively
+// aliases for the same path, and programs may refer to to either of them).
+// This should make all libraries and forked processes use the same.
+func SetTempDir(path string) (err error) {
+	var tempDir string
+	if tempDir, err = filepath.Abs(path); err != nil {
+		return err
+	}
+	if runtime.GOOS == "windows" {
+		if err = os.Setenv("TMP", tempDir); err != nil {
+			return err
+		}
+		if err = os.Setenv("TEMP", tempDir); err != nil {
+			return err
+		}
+	} else {
+		return os.Setenv("TMPDIR", tempDir)
+	}
+	return nil
+}

fs/config/configflags/configflags.go

@@ -6,6 +6,7 @@ package configflags
 import (
 	"log"
 	"net"
+	"os"
 	"strconv"
 	"strings"
 
@@ -23,6 +24,7 @@ var (
 	verbose         int
 	quiet           bool
 	configPath      string
+	tempDir         string
 	dumpHeaders     bool
 	dumpBodies      bool
 	deleteBefore    bool
@@ -47,6 +49,7 @@ func AddFlags(ci *fs.ConfigInfo, flagSet *pflag.FlagSet) {
 	flags.IntVarP(flagSet, &ci.Transfers, "transfers", "", ci.Transfers, "Number of file transfers to run in parallel.")
 	flags.StringVarP(flagSet, &configPath, "config", "", config.GetConfigPath(), "Config file.")
 	flags.StringVarP(flagSet, &config.CacheDir, "cache-dir", "", config.CacheDir, "Directory rclone will use for caching.")
+	flags.StringVarP(flagSet, &tempDir, "temp-dir", "", os.TempDir(), "Directory rclone will use for temporary files.")
 	flags.BoolVarP(flagSet, &ci.CheckSum, "checksum", "c", ci.CheckSum, "Skip based on checksum (if available) & size, not mod-time & size")
 	flags.BoolVarP(flagSet, &ci.SizeOnly, "size-only", "", ci.SizeOnly, "Skip based on size only, not mod-time or checksum")
 	flags.BoolVarP(flagSet, &ci.IgnoreTimes, "ignore-times", "I", ci.IgnoreTimes, "Don't skip files that match size and time - transfer all files")
@@ -278,6 +281,11 @@ func SetFlags(ci *fs.ConfigInfo) {
 		log.Fatalf("--config: Failed to set %q as config path: %v", configPath, err)
 	}
 
+	// Set path to temp dir
+	if err := config.SetTempDir(tempDir); err != nil {
+		log.Fatalf("--temp-dir: Failed to set %q as temp dir: %v", tempDir, err)
+	}
+
 	// Set whether multi-thread-streams was set
 	multiThreadStreamsFlag := pflag.Lookup("multi-thread-streams")
 	ci.MultiThreadSet = multiThreadStreamsFlag != nil && multiThreadStreamsFlag.Changed