Transmission

From ArchWiki

Transmission is a light-weight and cross-platform BitTorrent client.

Installation

There are three packages providing the transmission client:

There are also various third-party clients to connect to the daemon with:

Configuring the GUI version

Both GUI versions, transmission-gtk and transmission-qt, can function autonomously without a formal back-end daemon.

GUI versions are configured to work out-of-the-box, but the user may wish to change some of the settings. The default path to the GUI configuration files is ~/.config/transmission.

A guide to configuration options can be found on Transmission's Github.

Transmission daemon and CLI

The commands for transmission-cli are:

transmission-daemon
starts the daemon.
transmission-remote
invokes the CLI for the daemon, whether local or remote, followed by the command you want the daemon to execute.
transmission-show
returns information on a given torrent file.
transmission-create
creates a new torrent.
transmission-edit
add, delete, or replace a tracker's announce URL.
transmission-cli
(deprecated in favor of transmission-remote) starts a non-daemonized local instance of transmission, for manually downloading a torrent.
tremc
(requires tremc-gitAUR) starts the curses interface for the daemon, whether local or remote.

Starting and stopping the daemon

Transmission's daemon can be run:

  • As the user transmission, by starting/enabling transmission.service. The user can be changed as explained in #Choosing a user.
  • As your own user, by running under your user name:
$ transmission-daemon

Starting the daemon will create an initial configuration file. See #Configuring the daemon.

The daemon can then be stopped with: 

$ pkill -3 transmission-daemon

An alternative option to stop Transmission is to use the transmission-remote command: 

$ transmission-remote --exit

Reducing journal spam

Running transmission-daemon can lead to a lot of unwanted journal entries. Output can be filtered by starting it with a small wrapper script. The following example also provides some notifications: 

transwrap.sh
#!/bin/zsh
killall transmission-daemon 2> /dev/null
transmission-daemon --foreground --log-info 2>&1 | while read line; do
	echo $line |
		grep -v "announcer.c:\|platform.c:\|announce done (tr-dht.c:" |
		grep -v "Saved.*variant.c:" |
		while read line; do
			echo $line | grep -q "Queued for verification (verify.c:" &&
				notify-send --app-name="Transmission Started" "${line#* * }"
			echo $line | grep -q "changed from .Incomplete. to .Complete." &&
				notify-send --app-name="Transmission Complete" "${line#* * }"
			echo $line | systemd-cat --identifier="TransWrap" --priority=5
		done 2>&1 > /dev/null
	done&disown

Run only while connected to network

Netctl

It may be desirable to run transmission only on certain networks. The following script checks that the connection is to a list of authorized networks and then proceeds to launch transmission-daemon. 

/etc/netctl/hooks/90-transmission.sh
#!/bin/bash

# The SSIDs for which we enable this.
declare -A ssids=(
    ["network_1"]=y
    ["network_2"]=y
)

if [[ ${ssids[$SSID]} ]]; then
    case $ACTION in
        CONNECT|REESTABLISHED)
            # Need to wait, otherwise doesn't seem to bind to 9091.
            sleep 30
            systemctl start transmission
            ;;
        *)
            systemctl stop transmission
            ;;
    esac
fi

Choosing a user

Choose how you want to run transmission:

  • As a separate user, transmission by default (recommended for increased security).

By default, transmission creates a user and a group transmission, with its home files at /var/lib/transmission/, and runs as this "user". This is a security precaution, so transmission, and its downloads, have no access to files outside of /var/lib/transmission/. Configuration, operation, and access to downloads needs to be done with "root" privileges (e.g. by using sudo).

  • Under your own user. To set this up, override the provided service file and specify your username:
/etc/systemd/system/transmission.service.d/username.conf
[Service]
User=your_username

Configuring the daemon

Create an initial configuration file by starting the daemon.

  • If running Transmission under the username transmission, the configuration file will be located at /var/lib/transmission/.config/transmission-daemon/settings.json.
  • If running Transmission under your own username, the configuration file will be located at ~/.config/transmission-daemon/settings.json.

One can customize the daemon by using a Transmission client or using the included web interface accessible via http://localhost:9091 in a supported browser.

A guide to configuration options can be found on the Transmission web site: https://github.com/transmission/transmission/blob/main/docs/Editing-Configuration-Files.md

Note:
  • If you want to edit the configuration manually using a text editor, stop the daemon first; otherwise, it would overwrite its configuration file when it closes.
  • Alternatively, the daemon can be instructed to reload its configuration with SIGHUP, by running kill -s SIGHUP $(pidof transmission-daemon).

A recommendation for those running under username transmission is to create a shared download directory with the correct permissions to allow access to both the transmission user and system users, and then to update the configuration file accordingly. For example: 

# mkdir /mnt/data/torrents
# chown -R facade:transmission /mnt/data/torrents
# chmod -R 775 /mnt/data/torrents

Now /mnt/data/torrents will be accessible for the system user facade and for the transmission group to which the transmission user belongs. Making the target directory world read/writable is highly discouraged (i.e. do not chmod the directory to 777). Instead, give individual users/groups appropriate permissions to the appropriate directories.

Note: If /mnt/data/torrents is located on a removable device, e.g. with an /etc/fstab entry with the option nofail, Transmission will complain that it cannot find your files. To remedy this, you can add RequiresMountsFor=/mnt/data/torrents to /etc/systemd/system/transmission.service.d/transmission.conf in the section [Unit].

An alternative is to add your user to the transmission group (#usermod -a -G transmission yourusername) and then modify the permissions on the /var/lib/transmission and /var/lib/transmission/Downloads directories to allow rwx access by members of the transmission group.

Host whitelist

If you plan to access the Transmission daemon over the network using the server's hostname, you need to add this hostname to rpc-host-whitelist in settings.json. Otherwise, you will get a "421 Misdirected Request" error when accessing the server.

If you connect to the daemon using the server's IP-address, this is not required.

Watch dir

If you want to Automatically add .torrent files from a folder, but you find that the watch-dir and watch-dir-enabled options set in the configuration file do not work, you can start the transmission daemon with the flag -c /path/to/watch/dir.

If you are using systemd, edit the transmission.service unit as described in systemd#Editing provided units.

Enable IPv6

By default, the daemon only listens for IPv4 connections. To also listen for IPv6 connections, change the rpc-bind-address option to "::" in settings.json.

CLI Examples

If you want to remove all finished torrents you can use the following command with your own username and password: 

# transmission-remote -n 'username:password' -l | grep 100% | awk '{print $1}'| paste -d, -s | xargs -i transmission-remote -t {} -r

Seed a torrent which has already been downloaded: 

# transmission-remote [HOST] --torrent=example.torrent -a example.torrent --verify --download-dir=/dir/to/folder --start

Notification

Stop transmission-daemon and add these in .config/transmission-daemon/settings.json: 

   "script-torrent-added-enabled": true,
   "script-torrent-added-filename": "path/to/transmission-handler.sh",
   "script-torrent-done-enabled": true,
   "script-torrent-done-filename": "path/to/transmission-handler.sh",

transmission-handler.sh
#!/bin/bash

percentage=$(transmission-remote -t $TR_TORRENT_ID -l | awk -v ID="$TR_TORRENT_ID" '$0 ~ ID{print $2}')

if [ $percentage != "100%" ]
then
     notify-send --app-name="Transmission Started" "Transmission: started $TR_TORRENT_NAME"
else
     notify-send --app-name="Transmission Complete" "Transmission: downloaded $TR_TORRENT_NAME"
fi

Web interface

The GUI way

Once Transmission is installed, you can easily set up the web interface. All you need to do is click the edit menu and select preferences. Click the Remote tab and enable Allow remote access.

Here, you have the opportunity to change the default listening port from 9091.

Check the Use authentication and fill in a username and password so that authentication can be used.

To increase security, you can restrict access from any IP address by enabling Only allow these IP addresses.

Now you are ready to launch the web interface by either clicking on the Open web client, which makes your default web browser open it, or manually reaching http://TARGET_IP_ADDRESS:PORT with any supported web browser.

If you have not changed the listening port, the default one is 9091. In this case, the link is http://localhost:9091

Note: Keep in mind that transmission-cli must be installed

The CLI way

You do not need a graphical interface to set up the web interface, the daemon offers the very same options. You can reach the web interface without specifing any flags. See #Starting and stopping the daemon

Nevertheless, you can specify everything that you see in the previous section: 

$ transmission-daemon --auth --username arch --password linux --port 9091 --allowed "127.0.0.1"

is equivalent to 

$ transmission-daemon -t -u arch -v linux -p 9091 -a "127.0.0.1"
Note: If you set a user and password, all following commands to transmission-remote will need authentication with --auth username:password. See: transmission-remote commands are erroring with Unauthorized user

Optional web UI theme

If the default user interface of the web app seems outdated and less fancy than expected, try using https://git.eigenlab.org/sbiego/transmission-web-soft-theme for a simple CSS theme.

https://github.com/ronggang/transmission-web-control also provides a full replacement that can coexist with the default UI.

Usage as makepkg DLAGENT

Transmission can be used as magnet download agent for makepkg with the transmission-dlagentAUR download agent.

Magnet URIs need their prefix to be changed from magnet:? to magnet://.

Troubleshooting

Cannot access the daemon over the network

The daemon is started after network.service was initialised. However, if you enable the service dhcpcd as opposed to the device-specific service, such as dhcpcd@enp1s0.service for example, it may happen that Transmission is started too early and cannot bind to the network interface. Thus, the web interface is unreachable. A possible solution is to add the Requires line to the unit's configuration file: 

/etc/systemd/system/transmission.service.d/fixdep.conf
[Unit]
Requires=network.target

Web interface cannot be reached

404: Not Found

Couldn't find Transmission's web interface files!

Users: to tell Transmission where to look, set the TRANSMISSION_WEB_HOME environment variable to the folder where the web interface's index.html is located.

Package Builders: to set a custom default at compile time, #define PACKAGE_DATA_DIR in libtransmission/platform.c or tweak tr_getClutchDir () by hand.

Even if you use the graphical interface, you still need to install transmission-cli in order for web interface to work.

Failed to set send/receive buffer

Transmission might display either of these messages in the journal on startup: 

UDP Failed to set receive buffer: requested 4194304, got 425984
UDP Failed to set send buffer: requested 1048576, got 425984

These can be fixed by setting net.core.rmem_max=4194304 and net.core.wmem_max=1048576 with sysctl.

transmission-remote frequently times out or web interface is unresponsive

Transmission does not handle disk IO asynchronously, causing it to become unresponsive when doing heavy writes, see [1]. Consider putting transmission's download directory on faster storage, such as an ssd instead of an hdd.

Missing tray icon for transmission-gtk

Tray icon for GTK 4 version is not working for now. There is an option to use the GTK 3 version transmission-gtk3AUR.

401: Unauthorized

The following error may appear when using transmission-remote after setting a username and password for the web interface: 

< h1>401: Unauthorized\Unauthorized User

This happens because a username and password were set. After this, all commands from transmission-remote must be authenticated. See: transmission-remote commands are erroring with Unauthorized user

See also