Although systemd has been the object of many controversies, to the point the some distributions were forked just to get rid of it (see Devuan, a fork of Debian which, by default, replaces systemd with sysvinit), in the end it has become the de-facto standard init system in the Linux world.

In this tutorial we will see how a systemd service is structured, and we will learn how to create one.

In this tutorial you will learn:

• What is a service unit..
• What are the sections of a service unit.
• What are the most common options which can be used in each section.
• What are the different types of service that can be defined.

 

Software Requirements and Conventions Used

Software Requirements and Linux Command Line Conventions

Category	Requirements, Conventions or Software Version Used
System	A GNU/Linux distribution which uses systemd as init system
Software	systemd
Other	Root permissions are required to install and manage a service.
Conventions	# – requires given linux commands to be executed with root privileges either directly as a root user or by use of sudo command $ – requires given linux commands to be executed as a regular non-privileged user

The systemd init system

All the major distributions, such as Rhel, CentOS, Fedora, Ubuntu, Debian and Archlinux, adopted systemd as their init system. Systemd, actually, is more than just an init system, and that’s one of the reasons why some people are strongly against its design, which goes against the well established unix motto: “do one thing and do it well”. Where other init systems use simple shell script to manage services, systemd uses its own .service files (units with the .service suffix): in this tutorial we will see how they are structured and how to create and install one.

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Anatomy of a service unit

What is a service unit? A file with the .service suffix contains information about a process which is managed by systemd. It is composed by three main sections:

• [Unit]: this section contains information not specifically related to the type of the unit, such as the service description
• [Service]: contains information about the specific type of the unit, a service in this case
• [Install]: This section contains information about the installation of the unit

Let’s analyze each of them in detail.

The [Unit] section

The [Unit] section of a .service file contains the description of the unit itself, and information about its behavior and its dependencies: (to work correctly a service can depend on another one). Here we discuss some of the most relevant options which can be used in this section

The “Description” option

First of all we have the Description option. By using this option we can provide a description of the unit. The description will then appear, for example, when calling the systemctl command, which returns an overview of the status of systemd. Here it is, as an example, how the description of httpd service is defined on a Fedora system:

[Unit]
Description=The Apache HTTP Server

The “After” option

By using the After option, we can state that our unit should be started after the units we provide in the form of a space-separated list. For example, observing again the service file where the Apache web service is defined, we can see the following:

After=network.target remote-fs.target nss-lookup.target httpd-init.service

The line above instructs systemd to start the service unit httpd.service only after the network, remove-fs, nss-lookup targets and the httpd-init service.

Specifying hard dependencies with “Requires”

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As we briefly mentioned above, a unit (a service in our case) can depend on other units (not necessarily “service” units) to work correctly: such dependencies can be declared by using the Requires option.

If any of the units on which a service depends fails to start, the activation of the service it’s stopped: this is why those are called hard dependencies. In this line, extracted from the service file of the avahi-daemon, we can see how it is declared as dependent from the avahi-daemon.socket unit:

Requires=avahi-daemon.socket

Declaring “soft” dependencies with “Wants”

We just saw how to declare the so called “hard” dependencies for the service by using the Requires option; we can also list “soft” dependencies by using the Wants option.

What is the difference? As we said above, if any “hard” dependency fails, the service will fail itself; a failure of any “soft” dependency, however, doesn’t influence what happens to the dependent unit. In the provided example, we can see how the docker.service unit has a soft dependency on the docker-storage-setup.service one:

[Unit]
Wants=docker-storage-setup.service

The [Service] section

In the [Service] section of a service unit, we can specify things as the command to be executed when the service is started, or the type of the service itself. Let’s take a look at some of them.

Starting, stopping, and reloading a service

A service can be started, stopped, restarted or reloaded. The commands to be executed when performing each of these actions can be specified by using the related options in the [Service] section.

The command to be executed when a service starts, is declared by using the ExecStart option. The argument passed to the option can also be the path to a script. Optionally, we can declare commands to be executed before and after the service is started, by using the ExecStartPre and ExecStartPost options respectively. Here is the command used to start the NetworkManager service:

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---

[Service]
ExecStart=/usr/sbin/NetworkManager --no-daemon

In a similar fashion, we can specify the command to be executed when a service is reloaded or stopped, by using the ExecStop and ExecReload options. Similarly to what happens with ExecStartPost, a command or multiple commands to be launched after a process is stopped, can be specified with the ExecStopPost option.

The type of the service

Systemd defines and distinguish between some different type of services depending on their expected behavior. The type of a service can be defined by using the Type option, providing one of these values:

• simple
• forking
• oneshot
• dbus
• notify

The default type of a service, if the Type and Busname options are not defined, but a command is provided via the ExecStart option, is simple. When this type of service is set, the command declared in ExecStart is considered to be the main process/service.

The forking type works differently: the command provided with ExecStart is expected to fork and launch a child process, which will become the main process/service. The parent process it’s expected to die once the startup process is over.

The oneshot type is used as the default if the Type and ExecStart options are not defined. It works pretty much like simple: the difference is that the process is expected to finish its job before other units are launched. The unit, however, it’s still considered as “active” even after the command exits, if the RemainAfterExit option is set to “yes” (the default is “no”).

The next type of service is dbus. If this type of service is used, the daemon is expected to get a name from Dbus, as specified in the BusName option, which in this case, becomes mandatory. For the rest it works like the simple type. Consequent units, however, are launched only after the DBus name is acquired.

Another process works similarly to simple, and it is notify: the difference is that the daemon is expected to send a notification via the sd_notify function. Only once this notification is sent, consequent units are launched.

Set process timeouts

By using specific options, it’s possible to define some timeouts for the service. Let’s start with RestartSec: by using this option, we can setup the amount of time (by default in seconds) systemd should wait before restarting a service. A timespan can also be used as a value for this option, as “5min 20s”. The default is 100ms.

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The TimeoutStartSec and TimeoutStopSec options can be used to specify, respectively, the timeout for a service startup and stop, in seconds. In the first case, if after the specified timeout the daemon startup process it’s not completed, it will be considered to be failed.

In the second case, if a service is to be stopped but is not terminated after the specified timeout, first a SIGTERM and then, after the same amount of time, a SIGKILL signal are sent to it. Both options accepts also a timespan as a value and can be configured at once, with a shortcut: TimeoutSec. If infinity is provided as a value, the timeouts are disabled.

Finally, we can setup the limit for the amount of time a service can run, using the RuntimeMaxSec. If a service exceeds this timeout, it’s terminated and considered as failed.

The [Install] section

In the [install] section, we can use options related to the service installation. For example, by using the Alias option, we can specify a space separated list of aliases to be used for the service when using the systemctl commands (except enable).

Similarly to what happens with the Requires and Wants options in the [Unit] section, to establish dependencies, in the [install] section, we can use RequiredBy and WantedBy. In both cases we declare a list of units which depend on the one we are configuring: with the former option they will be hard-dependent on it, with the latter they will be considered only as weak-dependent. For example:

[Install]
WantedBy=multi-user.target

With the line above we declared that the multi-user target has a soft dependency on our unit. In systemd terminology, units ending with the .target suffix, can be associated with what were called runtimes in other init systems as Sysvinit. In our case, then, the multi-user target, when reached, should include our service.

Creating and installing a service unit

There are basically two places in the filesystem where systemd service units are installed: 

 

U.S.A
City	PSTN Number	Sponsor	Notes
Allentown	+1-484-2233755	DIDWW	2 concurrent calls supported
Anaheim, CA	+1-714-333-0397	LES.NET
Anaheim, CA	+1-714-400-0575	Callcentric
Arlington	+1-817-5246777	DIDWW	2 concurrent calls supported
Atlanta	+1-678-3999699	DIDWW	2 concurrent calls supported
Atlanta, GA	+1-404-478-6460	Callcentric
Aurora	+1-720-2627827	DIDWW	2 concurrent calls supported
Aurora, IL	+1-630-405-0745	Callcentric
Baltimore	+1-443-5247788	DIDWW	2 concurrent calls supported
Baltimore, MD	+1-443-455-0697	LES.NET
Baltimore, MD	+1-443-524-7370	Callcentric
Birmingham	+1-205-757-0797	LES.NET
Boise	+1-208-9068433	DIDWW	2 concurrent calls supported
Boise, ID	+1-208-906-1197	LES.NET
Boston	+1-617-8614466	DIDWW	2 concurrent calls supported
Boston, MA	+1-617-399-8298	Callcentric
Brooklyn	+1-347-6024544	DIDWW	2 concurrent calls supported
Buffalo, NY	+1-716-200-1692	LES.NET
Burbank, CA	+1-818-688-2797	LES.NET
Canoga Park	+1-818-9364699	DIDWW	2 concurrent calls supported
Chicago	+1-773-8191961	DIDWW	2 concurrent calls supported
Chicago, IL	+1-312-205-6444	Callcentric
Cleveland	+1-216-4521466	DIDWW	2 concurrent calls supported
Colorado Springs	+1-719-6457433	DIDWW	2 concurrent calls supported
Dallas	+1-214-4477120	DIDWW	2 concurrent calls supported
Dallas, TX	+1-214-261-9940	Callcentric
Denver	+1-303-9973255	DIDWW	2 concurrent calls supported
Denver, CO	+1-303-997-1197	LES.NET
Detroit	+1-313-3555705	DIDWW	2 concurrent calls supported
Fort Lauderdale	+1-954-6532113	DIDWW	2 concurrent calls supported
Fort Lauderdale, FL	+1-954-607-4525	Callcentric
Fremont-Newark, CA	+1-510-248-0397	LES.NET
Hollywood	+1-954-3747555	DIDWW	2 concurrent calls supported
Houston	+1-713-5548398	DIDWW	2 concurrent calls supported
Houston, TX	+1-832-369-6975	Callcentric
Indianapolis	+1-317-7596488	DIDWW	2 concurrent calls supported
Jacksonville, FL	+1-904-647-0897	LES.NET
Jacksonville, FL	+1-904-239-3990	Callcentric
Jersey City	+1-201-984-1823	LES.NET
Keys, FL	+1-305-890-1597	LES.NET
Keys, FL	+1-305-359-4571	Callcentric
Las Vegas	+1-702-7890530	DIDWW	2 concurrent calls supported
Las Vegas, NV	+1-702-553-2797	LES.NET
Los Angeles, CA	+1-323-2077414	DIDWW	2 concurrent calls supported
Los Angeles, CA	+1-323-209-2868	Routed Systems
Los Angeles, CA	+1-213-514-5397	LES.NET
Los Angeles, CA	+1-323-375-2897	LES.NET
Los Angeles, CA	+1-213-258-4475	Callcentric
Miami	+1-954-6074507	DIDWW	2 concurrent calls supported
Miami, FL	+1-305-537-5650	Callcentric
Michigan	+1-616-608-0509	Timmins Technologies, LLC
Michigan	182 Numbers	Telesthetic
Nassau, NY	+1-516-717-1635	Callcentric
New York	+1-212-4611066	DIDWW	2 concurrent calls supported
New York, NY	+1-646-291-2168	LES.NET
New York, NY	+1-646-810-9280	Callcentric
Norwalk, CA	+1-562-262-0897	LES.NET
Oakland Berkley, CA	+1-510-495-6397	LES.NET
Oakland Berkley, CA	+1-510-280-1620	Callcentric
Oakland Trinidad	+1-510-544-4497	LES.NET
Ogden, UT	+1-801-823-1197	LES.NET
Orlando, FL	+1-321-445-0797	LES.NET
Orlando, FL	+1-321-251-1890	Callcentric
Palo Alto	+1-650-644-1997	LES.NET
Pasadena, CA	+1-626-243-2197	LES.NET
Philadelphia, PA	+1-267-861-0797	LES.NET
Philadelphia, PA	+1-215-279-5938	Callcentric
Phoenix, AZ	+1-602-9267447	DIDWW	2 concurrent calls supported
Phoenix, AZ	+1-602-427-5727	Callcentric
Pittsburgh, PA	+1-412-360-7797	LES.NET
Portland, OR	+1-503-334-0597	LES.NET
Provo, UT	+1-801-877-1197	LES.NET
Reno, NV	+1-775-562-4697	LES.NET
Sacramento, CA	+1-916-209-4599	Routed Systems
Sacramento, CA	+1-916-313-3897	LES.NET
Sacramento, CA	+1-916-307-5151	Callcentric
Salt Lake City, UT	+1-801-618-0497	LES.NET
San Diego,CA	+1-619-393-1797	LES.NET
San Diego, CA	+1-619-684-3139	Callcentric
San Francisco	+1-415-5207622	DIDWW	2 concurrent calls supported
San Francisco, CA	+1-415-376-7297	LES.NET
San Francisco, CA	+1-415-594-0355	Callcentric
San Jose, CA	+1-408-538-2197	LES.NET
San Jose, CA	+1-408-625-4997	Callcentric
San Mateo	+1-650-523-6897	LES.NET
San Rafael	+1-415-223-4197	LES.NET
Santa Barbara, CA	+1-805-456-8597	LES.NET
Santa Cruz, CA	+1-831-480-3997	LES.NET
Santa Monica, CA	+1-310-862-5297	LES.NET
Sarasota, FL	+1-941-487-7697	LES.NET
Sarasota, FL	+1-941-296-7097	Callcentric
Seattle, WA	+1-206-829-6497	LES.NET
Seattle, WA	+1-360-526-0602	IPKall
Spokane, WA	+1-509-931-0297	LES.NET
Tacoma, WA	+1-253-617-4597	LES.NET
Tallahassee, FL	+1-850-254-7290	Callcentric
Tampa, FL	+1-813-200-5979	Callcentric
Torrance, CA	+1-310-294-8397	LES.NET
Twin Cities, MN	+1-612-604-4274	Callcentric
Walnut Creek	+1-925-891-8297	LES.NET
Washington DC	+1-202-8214808	DIDWW	2 concurrent calls supported
Washington DC	+1-202-552-1297	LES.NET
Washington DC	+1-202-821-4740	Callcentric
West Palm Beach, FL	+1-561-909-2899	Callcentric
Wilmington, DE	+1-302-824-0697	LES.NET
Wilmington, DE	+1-302-442-7167	Callcentric

MS Store: https://apps.microsoft.com/store/detail/%D0%BE%D0%BA/9WZDNCRFJ1X9

При поиске в Магазине, выбрать "Available on Mobile", иначе можете получить пустой результат поиска.

Есть поддержка XMPP:

 

Для того, чтобы подключиться к Jabber протоколу в "Одноклассниках", нужно уточнить свой id в этой социальной сети в настройках профиля на сайте. 

 

Этот id необходимо ввести в настройках IM клиента в поле username/учетная запись, а в качестве домена/сервера указать odnoklassniki.ru. Если вместо двух раздельных полей клиент требует ввести JID в одно поле, то это - id@odnoklassniki.ru.

 

В поле "пароль" нужно ввести пароль от профиля на "Одноклассниках".

 

Иногда также требуется указать адрес сервера и порт вручную - это xmpp.odnoklassniki.ru и 5222.

логин 1234567891@odnoklassniki.ru
пароль *********
сервер/хост xmpp.odnoklassniki.ru
порт 5222

https://vk.com/topic-119963489_34120834

 

Workaround:

 

Let's say your Microsoft account email is xxx@hotmail.com

 

Remove this account from the list of email accounts but leave it as is as Microsoft account.

 

At this point, your Microsoft account xxx@hotmail.com will be used only for MS Store and OneDrive.

 

Now second step:

 

1. Create ActiveSync account (Accounts-->Email & Apps accounts->Add an account->Advanced setup->Exchange ActiveSync) with following parameters:

 

email: xxx@hotmail.com 

User name: xxx@hotmail.com 

password: your account password 

Domain: empty or hotmail.com or outlook.com (the same as a domain part of your email)

Account name: "xxx@hotmail.com ActiveSync" (without quotes)
Server (if asked): m.hotmail.com

SSL: yes

Synchronize email, contact and calendar: YES

 

2. In calendar and contact settings enable displaying contacts and calendar from account xxx@hotmail.com ActiveSync