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| author | Laurent Bercot <ska-skaware@skarnet.org> | 2023-04-23 01:43:54 +0000 |
|---|---|---|
| committer | Laurent Bercot <ska@appnovation.com> | 2023-04-23 01:43:54 +0000 |
| commit | 9f87783018ca824019413132e099f696af9e44d3 (patch) | |
| tree | 370197158418e6448d0eac85d8ebc4ad810d3737 | |
| parent | 146da0d33300e8200537fb9b73ce1985a338f746 (diff) | |
| download | s6-9f87783018ca824019413132e099f696af9e44d3.tar.xz | |
Add systemd unit conversion guide page
Signed-off-by: Laurent Bercot <ska@appnovation.com>
| -rw-r--r-- | doc/unit-conversion.html | 1399 |
1 files changed, 1399 insertions, 0 deletions
diff --git a/doc/unit-conversion.html b/doc/unit-conversion.html new file mode 100644 index 0000000..09d5670 --- /dev/null +++ b/doc/unit-conversion.html @@ -0,0 +1,1399 @@ +<html> + <head> + <meta name="viewport" content="width=device-width, initial-scale=1.0" /> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>s6: how to convert systemd unit files to an s6 installation</title> + <meta name="Description" content="s6: how to convert systemd unit files to an s6 installation" /> + <meta name="Keywords" content="s6 systemd unit files configuration conversion porting" /> + <!-- <link rel="stylesheet" type="text/css" href="//skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6</a><br /> +<a href="//skarnet.org/software/">Software</a><br /> +<a href="//skarnet.org/">skarnet.org</a> +</p> + +<h1> How to convert systemd unit files to an s6 installation </h1> + +<p> + Converting a set of services managed by <a href="https://systemd.io/">systemd</a> +to a set of services managed by <a href="index.html">s6</a> is +a recurring question on our support channels, and having an automated conversion tool +parsing a set of <a href="https://man7.org/linux/man-pages/man5/systemd.unit.5.html">systemd +unit files</a> and outputting a set of <a href="servicedir.html">s6 +service directories</a> or +<a href="//skarnet.org/software/s6-rc/s6-rc-compile.html#source">s6-rc service +definition directories</a> would be extremely useful to people who want to migrate to +s6 but have an existing base of services running under systemd. +</p> + +<p> + Unfortunately, automating such a conversion is extremely difficult. The main +reason for this is that systemd and s6 are architectured in very different ways: +how they view a set of services, how they modelize a machine, what kind of solution +they bring to a given problem, and the extent of what they're supposed to manage +— there are few similarities between how systemd and s6 operate. As a +consequence, the way systemd maps a set of services into unit files is not +isomorphic to the way s6 does, so translating a setup between systemd and s6 +requires intelligence. It is not possible to write an automated tool that converts +a set of services accurately and idiomatically without doing a full, deep system +analysis - and writing such a tool would be a huge undertaking. +</p> + +<p> + Fortunately, in practice, most unit files only use a small subset of all the +theoretically supported directives: most services that run under systemd can be +converted to run under s6 without too much trouble. So, depending on the exact +nature of the set of services, it may be possible to write a reasonable converter, +that is limited in what it supports but does not require a full understanding +of systemd or s6. +</p> + +<p> + This document targets people who think about writing a tool to automatically +convert a set of unit files to a set of s6 services and are trying to assess +its feasability and difficulty. We analyze all the directives that may appear +in a unit file for their services, and rate the difficulty of translating the +directive, i.e. the amount of complexity that would need to go into the +converter tool if that directive were to be supported. +</p> + +<p> + We rate difficulty on a scale from <strong>0</strong> to <strong>10</strong>. +A <strong>0</strong> means that the directive is irrelevant to s6 and can +be ignored. A <strong>1</strong> means that there is a straightforward, +one-for-one way of translating the systemd directive into s6 parlance. A +<strong>10</strong> means that the directive is so systemd-specific that it +is impossible to express it on an s6 system and the unit file cannot be +converted as is. A <strong>9</strong> means that it is theoretically possible +to convert, given infinite time and manpower to write a tool that analyzes +the systemd-managed system holistically and outputs an equivalent system +managed by s6, but in practice nobody's ever going to write such a tool. +</p> + +<hr /> + +<ul> + <li> + <a href="#by-directive">All the directives listed by the order in the +systemd documentation, with their difficulty</a> + <ul> + <li> <a href="#systemd.unit">in systemd.unit(5)</a> + <ul> + <li> <a href="#unit-section"><tt>[Unit]</tt> section</a> </li> + <li> <a href="#install-section"><tt>[Install]</tt> section</a> </li> + </ul> + </li> + <li> <a href="#systemd.service">in systemd.service(5)</a> + <ul> + <li> <a href="#service-section"><tt>[Service]</tt> section</a> </li> + </ul> + </li> + <li> <a href="#systemd.exec">in systemd.exec(5)</a> + <ul> + <li> <a href="#systemd.exec-paths">Paths</a> </li> + <li> <a href="#systemd.exec-identity">User/group identity</a> </li> + <li> <a href="#systemd.exec-security">Security</a> </li> + <li> <a href="#systemd.exec-mandatoryac">Mandatory access control</a> </li> + <li> <a href="#systemd.exec-properties">Process properties</a> </li> + <li> <a href="#systemd.exec-scheduling">Scheduling</a> </li> + <li> <a href="#systemd.exec-sandboxing">Sandboxing</a> </li> + <li> <a href="#systemd.exec-filtering">System call filtering</a> </li> + <li> <a href="#systemd.exec-environment">Environment</a> </li> + <li> <a href="#systemd.exec-logging">Logging and standard input/output</a> </li> + <li> <a href="#systemd.exec-credentials">Credentials</a> </li> + <li> <a href="#systemd.exec-sysv">System V compatibility</a> </li> + </ul> + </li> + <li> <a href="#systemd.kill">in systemd.kill(5)</a> </li> + </ul> + </li> + <li> + <a href="#by-difficulty">All the directives listed by their difficulty</a> + <ul> + <li> <a href="#difficulty-0">0</a> </li> + <li> <a href="#difficulty-1">1</a> </li> + <li> <a href="#difficulty-2">2</a> </li> + <li> <a href="#difficulty-3">3</a> </li> + <li> <a href="#difficulty-4">4</a> </li> + <li> <a href="#difficulty-5">5</a> </li> + <li> <a href="#difficulty-6">6</a> </li> + <li> <a href="#difficulty-7">7</a> </li> + <li> <a href="#difficulty-8">8</a> </li> + <li> <a href="#difficulty-9">9</a> </li> + <li> <a href="#difficulty-10">10</a> </li> + </ul> + </li> +</ul> + +<hr /> + +<h2 id="by-directive"> Difficulty by directive </h2> + +<p> + Use this section to answer the question: "I have this directive in my unit file, +how hard would it be to write a converter tool that processes this file?" +</p> + +<h3 id="systemd.unit"> + Directives documented in <a href="https://man7.org/linux/man-pages/man5/systemd.unit.5.html">systemd.unit(5)</a> +</h3> + +<h4 id="unit-section"> + <tt>[Unit]</tt> section +</h4> + +<ul> + <li> <tt>Description=</tt> : <strong>0</strong>. </li> + <p /> + <li> <tt>Documentation=</tt> : <strong>0</strong>. </li> + <p /> + <li> <tt>Wants=</tt> : <strong>3</strong>. Dependencies between services +are implemented via <a href="//skarnet.org/software/s6-rc/">s6-rc</a>; in order +to implement <tt>Wants=</tt>. the converter needs to target s6-rc, which is a +reasonable requirement for a complete set of services. However, <tt>Wants=</tt> +expresses weak dependencies, which are not supported by the current version of +s6-rc, so the exact nature of the dependency needs to be checked by hand. </li> + <p /> + <li> <tt>Requires=</tt> : <strong>2</strong>. The converter needs to +target <a href="//skarnet.org/software/s6-rc/">s6-rc</a>, but <tt>Requires=</tt> +dependencies map well to the s6-rc dependency model. </li> + <p /> + <li> <tt>Requisite=</tt> : <strong>3</strong>. systemd supports a lot of +weird types of dependencies that the current version of s6-rc does not (by +design). </li> + <p /> + <li> <tt>BindsTo=</tt> : <strong>3</strong>. Same. </li> + <p /> + <li> <tt>PartOf=</tt> : <strong>3</strong>. Same. </li> + <p /> + <li> <tt>Upholds=</tt> : <strong>0</strong>. In s6, services are upheld by +the supervisor, not by other services. </li> + <p /> + <li> <tt>Conflicts=</tt> : <strong>5</strong>. There are no negative +dependencies in the s6 world, and a converter tool would have to implement it +on top of the existing system. </li> + <p /> + <li> <tt>Before=</tt> : <strong>2</strong>. systemd loves to have a +zillion of keywords to express slightly different kinds of dependencies, and +only a small subset of all the possible combinations are useful. </li> + <p /> + <li> <tt>After=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>OnFailure=</tt> : <strong>5</strong>. Permanent failure is +a very exceptional state in s6, there are no hooks to do something when +permanent failure occurs; so a converter would need to add scripting around that. </li> + <p /> + <li> <tt>OnSuccess=</tt> : <strong>2</strong>. These are oneshot +dependencies. </li> + <p /> + <li> <tt>PropagatesReloadTo=</tt> : <strong>0</strong>. Under s6-rc +you can either reload a single service or the whole dependency chain that +starts at the service. Other configurations just make no sense. </li> + <p /> + <li> <tt>ReloadPropagatedFrom=</tt> : <strong>0</strong>. Same. </li> + <p /> + <li> <tt>PropagatesStopTo=</tt> : <strong>0</strong>. Same with stopping +a single service or a dependency chain of services. </li> + <p /> + <li> <tt>StopPropagatedFrom=</tt> : <strong>0</strong>. Same. </li> + <p /> + <li> <tt>JoinsNamespaceOf=</tt> : <strong>8</strong>. There are no +native s6 tools to manage namespaces. </li> + <p /> + <li> <tt>RequiresMountsFor=</tt> : <strong>4</strong>. Mounts are +not handled in a special way in s6, the converter would have to know +what service mounts what filesystem. </li> + <p /> + <li> <tt>OnFailureJobMode=</tt> : <strong>6</strong>. This is what +happens when you mix layers. </li> + <p /> + <li> <tt>IgnoreOnIsolate=</tt> : <strong>0</strong>. </li> + <p /> + <li> <tt>StopWhenUnneeded=</tt> : <strong>0</strong>. </li> + <p /> + <li> <tt>RefuseManualStart=</tt> : <strong>4</strong>. Would need +some scripting around. There's no reason to ever use that directive though. </li> + <p /> + <li> <tt>RefuseManualStop=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>AllowIsolate=</tt> : <strong>0</strong>. </li> + <p /> + <li> <tt>DefaultDependencies=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>CollectMode=</tt> : <strong>0</strong>. </li> + <p /> + <li> <tt>FailureAction=</tt> : <strong>3</strong>. Anything involving +permanent failure need to be scripted around, because s6 considers that +it is an extreme state that requires administrator attention and will +stop making automatic decisions. </li> + <p /> + <li> <tt>SuccessAction=</tt> : <strong>3</strong>. That's a oneshot +dependency, but systemd doesn't realize that. </li> + <p /> + <li> <tt>FailureActionExitStatus=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>SuccessActionExitStatus=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>JobTimeoutSec=</tt> : <strong>9</strong>. s6 has no +concept of jobs. </li> + <p /> + <li> <tt>JobRunningTimeoutSec=</tt> : <strong>9</strong>. Same. </li> + <p /> + <li> <tt>JobTimeoutAction=</tt> : <strong>9</strong>. Same. </li> + <p /> + <li> <tt>JobTimeoutRebootArgument=</tt> : <strong>9</strong>. Same. </li> + <p /> + <li> <tt>StartLimitIntervalSec=</tt> : <strong>3</strong>. s6 does +not limit start rate. It can stop a service that has a high <em>death</em> +rate: that's the configuration knob that makes sense. That directive can +be converted to check death interval instead. </li> + <p /> + <li> <tt>StartLimitBurst=</tt> : <strong>3</strong>. Same. </li> + <p /> + <li> <tt>StartLimitAction=</tt> : <strong>3</strong>. Same. </li> + <p /> + <li> <tt>RebootArgument=</tt> : <strong>5</strong>. Any "system mode" +action such as a reboot has no place in an s6 set of services anyway; +systemd obviously likes to mix unrelated layers. In the s6 world, the only +place where a reboot should occur is +<a href="//skarnet.org/software/s6-linux-init/">s6-linux-init</a>, and the +related scripting in <tt>rc.init</tt> files. </li> + <p /> + <li> <tt>SourcePath=</tt> : <strong>0</strong>. </li> + <p /> + <li> Conditions and Asserts: <strong>9</strong>. Most of these are tied to the +global machine state and absolutely not local to a given set of services. And +even for those that are not, what they do is change the whole service manager's +behaviour depending on some external dynamic state such as the existence of a +file in the filesystem — and that is entirely contrary to the s6 +philosophy of making services predictable and reproductble. </li> +</ul> + +<h4 id="install-section"> + <tt>[Install]</tt> section +</h4> + +<p> + Any directive under <tt>[Install]</tt> can be ignored, since it has no +meaning on the run-time behaviour of the service. So the difficulty is +<strong>0</strong>. However, an automatic converter would need to +analyze the whole installed service configuration, e.g. the links in +<tt>/etc/systemd/system/multi-user.target.wants/</tt>, in order to +understand the dependencies between services. systemd targets can +typically be converted into s6-rc bundles. +</p> + +<h3 id="systemd.service"> + Directives documented in <a href="https://man7.org/linux/man-pages/man5/systemd.service.5.html">systemd.service(5)</a> +</h3> + +<h4 id="service-section"> + <tt>[Service]</tt> section +</h4> + +<ul> + <li> <tt>Type=</tt> : depending on its type, a systemd "service" +can translate to wildly different things under s6. + <ul> + <li> <tt>simple</tt> : <strong>1</strong>. </li> + <li> <tt>exec</tt> : <strong>1</strong>. </li> + <li> <tt>forking</tt> : <strong>2</strong>. This type is strongly discouraged. </li> + <li> <tt>oneshot</tt> : <strong>1</strong>. </li> + <li> <tt>dbus</tt> : <strong>5</strong>. This type requires implementing dbus +management programs for s6. </li> + <li> <tt>notify</tt> : <strong>7</strong>. This type requires an implementation +of a compatibility server for +<a href="https://man7.org/linux/man-pages/man3/sd_notify.3.html"><tt>sd_notify()</tt></a>, +which is heavily tied to the monolithic systemd architecture and is difficult to support +in a modular system such as s6. It is much easier to modify the services themselves so +they use the <a href="notifywhenup.html">s6 readiness +notification mechanism</a> instead of sd_notify. </li> + <li> <tt>idle</tt> : <strong>0</strong>. This type is meaningless under s6 and +should be treated like <tt>simple</tt>. </li> + </ul> + </li> + <p /> + <li> <tt>ExitType=</tt> : again, it depends on the value. + <ul> + <li> <tt>main</tt> : <strong>1</strong>. </li> + <li> <tt>cgroup</tt> : <strong>3</strong>. This requires implementing, or +having access to, command-line cgroup tools. </li> + </ul> + </li> + <p /> + <li> <tt>RemainAfterExit=</tt> : <strong>0</strong>. </li> + <p /> + <li> <tt>GuessMainPid=</tt> : <strong>0</strong>. But don't use <tt>forking</tt> +if you can avoid it. </li> + <p /> + <li> <tt>PIDFile=</tt> : <strong>2</strong>. Same. </li> + <p /> + <li> <tt>BusName=</tt> : <strong>5</strong>. Avoid type <tt>dbus</tt> if possible. </li> + <p /> + <li> <tt>ExecStart=</tt> : <strong>2</strong>, with caveats. This is the bread and +butter of service definitions; all your services will likely have such a directive, and +the contents of <tt>ExecStart=</tt> will typically go into a run script (for longruns) or +an up file (for oneshots). However, since systemd hates simplicity, there are a number +of transformations that have to happen to the command line before it can be used in a +script, and in particular if the command has a <em>special executable prefix</em>. +Implementing these has its own difficulty ratings: + <ul> + <li> <tt>@</tt> : <strong>1</strong>. </li> + <li> <tt>-</tt> : <strong>1</strong>. </li> + <li> <tt>:</tt> : <strong>2</strong>. </li> + <li> <tt>+</tt> : <strong>5</strong>. </li> + <li> <tt>!</tt> : <strong>3</strong>. </li> + <li> <tt>!!</tt> : <strong>3</strong>. </li> + </ul> + </li> + <p /> + <li> <tt>ExecStartPre=</tt> : <strong>2</strong>. In order to have a strict +semantic equivalence with their systemd version, <tt>ExecStartPre=</tt> lines must +be implemented as s6-rc oneshots, and the whole unit file must be implemented as +a bundle. </li> + <p /> + <li> <tt>ExecStartPost=</tt> : <strong>2</strong>. Same. </li> + <p /> + <li> <tt>ExecCondition=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>ExecReload=</tt> : <strong>0</strong>. A reloading command that +does not involve restarting the service does not need the service manager as +a third-party. systemd cannot help inserting itself where it does not belong. </li> + <p /> + <li> <tt>ExecStop=</tt> : <strong>6</strong>. s6 only supports terminating +services via signals, so if a service needs a specific command to be stopped, +the converter needs to target an interface layer on top of s6 with a repository +of stop commands; such a layer would likely need to be on top of s6-rc as well +and a lot of complexity would ensue. Fortunately, a huge majority of services +support termination via signals and it is often easy to avoid relying on +<tt>ExecStop=</tt>. </li> + <p /> + <li> <tt>ExecStopPost=</tt> : <strong>2</strong>. These are the +<tt>down</tt> scripts of the <tt>ExecStartPre=</tt> oneshots. </li> + <p /> + <li> <tt>RestartSec=</tt> : <strong>2</strong>. s6 has no setting for that, +because it aims for maximum uptime; but there are still ways to implement that +bad idea. </li> + <p /> + <li> <tt>TimeoutStartSec=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>TimeoutStopSec=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>TimeoutAbortSec=</tt> : <strong>7</strong>. This would need a +watchdog implementation, in the server implementation of <tt>sd_notify()</tt>. </li> + <p /> + <li> <tt>TimeoutSec=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>TimeoutStartFailureMode=</tt> : <strong>0</strong> for +<tt>terminate</tt> and <tt>kill</tt>, <strong>7</strong> for <tt>abort</tt>. </li> + <p /> + <li> <tt>TimeoutStopFailureMode=</tt> : <strong>0</strong> for +<tt>terminate</tt> and <tt>kill</tt>, <strong>7</strong> for <tt>abort</tt>. </li> + <p /> + <li> <tt>RuntimeMaxSec=</tt> : <strong>4</strong>. This is the exact +opposite of what you need a process supervisor for, so s6 does not +implement it. It is best to run such a process (not a <em>service</em>) +outside of any kind of supervision framework. </li> + <p /> + <li> <tt>RuntimeRandomizedExtraSec=</tt> : <strong>4</strong>. Same. </li> + <p /> + <li> <tt>WatchdogSec=</tt> : <strong>7</strong>. Requires a watchdog +implementation in the very specific systemd way. </li> + <p /> + <li> <tt>Restart=</tt> : depends on the value. + <ul> + <li> <tt>no</tt> : <strong>2</strong>, but why use a process supervisor +in the first place? </li> + <li> <tt>on-success</tt> : <strong>2</strong>. </li> + <li> <tt>on-failure</tt> : <strong>2</strong>. </li> + <li> <tt>on-abnormal</tt> : <strong>2</strong>. </li> + <li> <tt>on-watchdog</tt> : <strong>7</strong>. Again, this requires +a watchdog implementation. </li> + <li> <tt>on-abort</tt> : <strong>2</strong>. </li> + <li> <tt>always</tt> : <strong>1</strong>. </li> + </ul> + </li> + <p /> + <li> <tt>SuccessExitStatus=</tt> : <strong>3</strong>. This can be easily +scripted, but supporting all the systemd formats is annoying. </li> + <p /> + <li> <tt>RestartPreventExitStatus=</tt> : <strong>1</strong>. This is +exactly what <a href="s6-permafailon.html">s6-permafailon</a> +is for. </li> + <p /> + <li> <tt>RestartForceExitStatus=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>RootDirectoryStartOnly=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>NonBlocking=</tt> : <strong>5</strong>. This requires an +emulation of systemd's socket activation. s6 provides the useful parts of +it, like a <a href="s6-fdholder-daemon.html">process +to hold file descriptors</a>, but the systemd-specific API around socket +activation, <a href="https://www.freedesktop.org/software/systemd/man/sd_listen_fds.html">sd_listen_fds(3)</a>, +still needs to be implemented. </li> + <p /> + <li> <tt>NotifyAccess=</tt> : <strong>1</strong> if <tt>none</tt>, <strong>7</strong> +otherwise, because it needs an implementation of <tt>sd_notify()</tt>. </li> + <p /> + <li> <tt>Sockets=</tt> : <strong>5</strong>. Requires an implementation +of systemd's socket activation. </li> + <p /> + <li> <tt>FileDescriptorStoreMax=</tt> : <strong>7</strong>. Requires an implementation +of <tt>sd_notify()</tt>; the fd store itself is native to s6. </li> + <p /> + <li> <tt>USBFunctionDescriptors=</tt> : <strong>9</strong>. This is +low-level machine management, not service management. </li> + <p /> + <li> <tt>USBFunctionStrings=</tt> : <strong>9</strong>. Same. </li> + <p /> + <li> <tt>OOMPolicy=</tt> : <strong>9</strong>. Same. </li> +</ul> + +<h3 id="systemd.exec"> + Directives documented in <a href="https://man7.org/linux/man-pages/man5/systemd.exec.5.html">systemd.exec(5)</a> +</h3> + +<h4 id="systemd.exec-paths"> + Paths +</h4> + +<ul> + <li> <tt>ExecSearchPath=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>WorkingDirectory=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>RootDirectory=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>RootImage=</tt> : <strong>6</strong>. I am discovering these +options in real time and shaking my head - systemd still manages to baffle me +with the amount of gratuitous ad-hoc that went into it. Still, this is +regular low-level programming for Linux, this is less difficult to implement than +systemd-specific stuff, that's why it only gets a 6. </li> + <p /> + <li> <tt>RootImageOptions=</tt> : <strong>6</strong>. Same. </li> + <p /> + <li> <tt>RootHash=</tt> : <strong>9</strong>. Please. </li> + <p /> + <li> <tt>RootHashSignature=</tt> : <strong>9</strong>. </li> + <p /> + <li> <tt>RootVerity=</tt> : <strong>9</strong>. </li> + <p /> + <li> <tt>MountAPIVFS=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>ProtectProc=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>ProcSubset=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>BindPaths=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>BindReadOnlyPaths=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>MountImages=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>ExtensionImages=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>ExtensionDirectories=</tt> : <strong>6</strong>. It's a full low-level +userspace implementation at this point. It's not very <em>complex</em>, the 6 feels +accurate, but it's a whole lot of work. This is how systemd maintains its +hegemony: not because it does incredible, awe-inspiring magic, but because it +substitutes its monolithic self to a whole ecosystem, imposes its own API, and +locks users in — people who want to smoothly transition away from systemd need +to implement <em>the whole shtick</em>, which is obviously a huge undertaking, as +the author of <a href="https://web.archive.org/web/20150516113530/http://uselessd.darknedgy.net/">uselessd</a> +can confirm. </li> +</ul> + +<h4 id="systemd.exec-identity"> + User/group identity +</h4> + +<ul> + <li> <tt>User=</tt> : <strong>3</strong>. This looks very simple, but is +treacherous, because <tt>User=</tt> is a mash of two very different features: +setting users <em>statically</em> (via numeric ID, which don't change meanings +between two invocations) and setting users <em>dynamically</em> (via user name, +which needs to be interpreted by +<a href="https://pubs.opengroup.org/onlinepubs/9699919799/functions/getpwnam.html">getpwnam(3)</a> +on every invocation of the service. s6 supports both, but since these are two +different things, the way to do them in s6 is different (statically setting the +UID and GID variables and calling +<a href="s6-applyuidgid.html">s6-applyuidgid -U</a>, +or calling <a href="s6-setuidgid.html">s6-setuidgid</a>). +This is the exact kind of small detail that makes writing an automatic converter more difficult +than it should be: the systemd unit file syntax is rife with semantic pitfalls, and managing +your way across it requires very close attention. </li> + <p /> + <li> <tt>Group=</tt> : <strong>3</strong>. Same. </li> + <p /> + <li> <tt>DynamicUser=</tt> : <strong>5</strong>. Of course this flag has an +<em>entirely</em> different meaning from setting users statically or dynamically, or +else it would be too easy to understand. No, this flag is about <em>allocating temporary +new users</em>, which is a prime example of overengineering. </li> + <p /> + <li> <tt>SupplementaryGroups=</tt> : <strong>1</strong>. Same. </li> + <p /> + <li> <tt>PAMName=</tt> : <strong>4</strong>. Requires PAM command-line +utilities. </li> +</ul> + +<h4 id="systemd.exec-capabilities"> + Capabilities +</h4> + +<ul> + <li> <tt>CapabilityBoundingSet=</tt> : <strong>4</strong>. This requires +command-line tools implementing capabilities. </li> + <p /> + <li> <tt>AmbientCapabilities=</tt> : <strong>4</strong>. Same. </li> +</ul> + +<h4 id="systemd.exec-security"> + Security +</h4> + +<ul> + <li> <tt>NoNewPrivileges=</tt> : <strong>4</strong>. Similar to capabilities, +this requires a command-line tool controlling the Linux-specific +<a href="https://man7.org/linux/man-pages/man2/prctl.2.html">prctl(2)</a> system +call. </li> + <p /> + <li> <tt>SecureBits=</tt> : <strong>4</strong>. Same. </li> +</ul> + +<h4 id="systemd.exec-mandatoryac"> + Mandatory access control +</h4> + +<ul> + <li> <tt>SELinuxContext=</tt> : <strong>5</strong>. This requires +command-line tools managing SELinux. </li> + <p /> + <li> <tt>AppArmorProfile=</tt> : <strong>5</strong>. Same, with AppArmor. </li> + <p /> + <li> <tt>SmackProcessLabel=</tt> : <strong>5</strong>. Same, with SMACK. +systemd needs to know and understand all the Linux security modules in order +to interact with them. s6 does not - it expects a service's run script to +perform all the needed process state changes and controls before executing +into the daemon. </li> +</ul> + +<h4 id="systemd.exec-properties"> + Process properties +</h4> + +<ul> + <li> <tt>LimitCPU=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LimitFSIZE=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LimitDATA=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LimitSTACK=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LimitCORE=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LimitRSS=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LimitNOFILE=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LimitAS=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LimitNPROC=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LimitMEMLOCK=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LimitLOCKS=</tt> : <strong>2</strong>. This resource limit +isn't natively supported by +<a href="//skarnet.org/software/s6/s6-softlimit.html">s6-softlimit</a>, but +it could appear in a future s6 version - and it's easy to add in any case. </li> + <p /> + <li> <tt>LimitSIGPENDING=</tt> : <strong>2</strong>. Same. </li> + <p /> + <li> <tt>LimitMSGQUEUE=</tt> : <strong>2</strong>. Same. </li> + <p /> + <li> <tt>LimitNICE=</tt> : <strong>2</strong>. Same. </li> + <p /> + <li> <tt>LimitRTPRIO=</tt> : <strong>2</strong>. Same. </li> + <p /> + <li> <tt>LimitRTTIME=</tt> : <strong>2</strong>. Same. </li> + <p /> + <li> <tt>UMask=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>CoredumpFilter=</tt> : <strong>4</strong>. Requires a +command-line tool around <a href="https://man7.org/linux/man-pages/man2/prctl.2.html">prctl(2)</a>. </li> + <p /> + <li> <tt>KeyringMode=</tt> : <strong>5</strong>. Requires +interaction with PAM and an understanding of keyrings. Fortunately, +practically nothing will need that. </li> + <p /> + <li> <tt>OOMScoreAdjust=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>TimerSlackNSec=</tt> : <strong>4</strong>. Requires a +command-line tool around <a href="https://man7.org/linux/man-pages/man2/prctl.2.html">prctl(2)</a>. </li> + <p /> + <li> <tt>Personality=</tt> : <strong>3</strong>. Requires a +command-line tool around <a href="https://man7.org/linux/man-pages/man2/personality.2.html">personality(2)</a>. </li> + <p /> + <li> <tt>IgnoreSIGPIPE=</tt> : <strong>2</strong>. </li> +</ul> + +<h4 id="systemd.exec-scheduling"> + Scheduling +</h4> + +<ul> + <li> <tt>Nice=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>CPUSchedulingPolicy=</tt> : <strong>3</strong>. Requires a +command-line tool around <a href="https://man7.org/linux/man-pages/man2/sched_setscheduler.2.html">sched_setscheduler(2)</a>. </li> + <p /> + <li> <tt>CPUSchedulingPriority=</tt> : <strong>3</strong>. Same. </li> + <p /> + <li> <tt>CPUSchedulingResetOnFork=</tt> : <strong>3</strong>. Same. </li> + <p /> + <li> <tt>CPUAffinity=</tt> : <strong>3</strong>. Requires a +command-line tool around <a href="https://man7.org/linux/man-pages/man2/sched_setaffinity.2.html">sched_setaffinity(2)</a>. </li> + <p /> + <li> <tt>NUMAPolicy=</tt> : <strong>3</strong>. Requires a +command-line tool around <a href="https://man7.org/linux/man-pages/man2/set_mempolicy.2.html">set_mempolicy(2)</a>. </li> + <p /> + <li> <tt>NUMAMask=</tt> : <strong>3</strong>. Same. </li> + <p /> + <li> <tt>IOSchedulingClass=</tt> : <strong>3</strong>. Requires a +command-line tool around <a href="https://man7.org/linux/man-pages/man2/ioprio_set.2.html">ioprio_set(2)</a>. </li> + <p /> + <li> <tt>IOSchedulingPriority=</tt> : <strong>3</strong>. Same. </li> +</ul> + +<h4 id="systemd.exec-sandboxing"> + Sandboxing +</h4> + +<p> + systemd gracefully turns off the sandboxing options on systems that +do not support the necessary functionality, so all these options can +be ignored (difficulty <strong>0</strong>) and the services will still +work. However, in order to actually implementing the sandboxing, it is +necessary to pair s6 with command-line tools that perform the required +process state changes by interfacing with namespaces, cgroups, seccomp, +or any other relevant feature of the Linux kernel, so for all these +directives the difficulty is somewhere between <strong>2</strong>, if +the tool already exists, and <strong>8</strong>, if it requires writing +a full container implementation from scratch. The following numbers are +only a rough guess. +</p> + +<ul> + <li> <tt>ProtectSystem=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>ProtectHome=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>RuntimeDirectory=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>StateDirectory=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>CacheDirectory=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LogsDirectory=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>ConfigurationDirectory=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>RuntimeDirectoryMode=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>StateDirectoryMode=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>CacheDirectoryMode=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>LogsDirectoryMode=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>ConfigurationDirectoryMode=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>RuntimeDirectoryPreserve=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>TimeoutCleanSec=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>ReadWritePaths=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>ReadOnlyPaths=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>InaccessiblePaths=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>ExecPaths=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>NoExecPaths=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>TemporaryFileSystem=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>PrivateTmp=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>PrivateDevices=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>PrivateNetwork=</tt> : <strong>8</strong>. </li> + <p /> + <li> <tt>NetworkNamespacePath=</tt> : <strong>8</strong>. </li> + <p /> + <li> <tt>PrivateIPC=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>IPCNamespacePath=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>PrivateUsers=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>ProtectHostname=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>ProtectClock=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>ProtectKernelTunables=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>ProtectKernelModules=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>ProtectKernelLogs=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>ProtectControlGroups=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>RestrictAddressFamilies=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>RestrictFilesystems=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>RestrictNamespaces=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>LockPersonality=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>MemoryDenyWriteExecute=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>RestrictRealtime=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>RestrictSUIDSGID=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>RemoveIPC=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>PrivateMounts=</tt> : <strong>5</strong>. </li> +</ul> + +<h4 id="systemd.exec-filtering"> + System call filtering +</h4> + +<ul> + <li> <tt>SystemCallFilter=</tt> : <strong>8</strong>. </li> + <p /> + <li> <tt>SystemCallErrorNumber=</tt> : <strong>8</strong>. </li> + <p /> + <li> <tt>SystemCallArchitectures=</tt> : <strong>8</strong>. </li> + <p /> + <li> <tt>SystemCallLog=</tt> : <strong>8</strong>. </li> +</ul> + +<h4 id="systemd.exec-environment"> + Environment +</h4> + +<ul> + <li> <tt>Environment=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>EnvironmentFile=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>PassEnvironment=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>UnsetEnvironment=</tt> : <strong>1</strong>. </li> +</ul> + +<h4 id="systemd.exec-logging"> + Logging and standard input/output +</h4> + +<ul> + <li> <tt>StandardInput=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>StandardOutput=</tt> : <strong>1</strong>, except +for <tt>journal</tt> which cannot be supported (<strong>10</strong>). </li> + <p /> + <li> <tt>StandardError=</tt> : same. </li> + <p /> + <li> <tt>StandardInputText=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>StandardInputData=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>LogLevelMax=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>LogExtraFields=</tt> : <strong>10</strong>. </li> + <p /> + <li> <tt>LogRateLimitIntervalSec=</tt> : <strong>10</strong>. </li> + <p /> + <li> <tt>LogRateLimitBurst=</tt> : <strong>10</strong>. </li> + <p /> + <li> <tt>LogFilterPatterns=</tt> : <strong>4</strong>. </li> + <p /> + <li> <tt>LogNamespace=</tt> : <strong>10</strong>. </li> + <p /> + <li> <tt>SyslogIdentifier=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>SyslogFacility=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>SyslogLevel=</tt> : <strong>2</strong>. </li> + <p /> + <li> <tt>SyslogLevelPrefix=</tt> : <strong>4</strong>. </li> + <p /> + <li> <tt>TTYPath=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>TTYReset=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>TTYVHangup=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>TTYRows=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>TTYColumns=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>TTYDisallocate=</tt> : <strong>3</strong>. </li> + <p /> +</ul> + +<h4 id="systemd.exec-credentials"> + Credentials +</h4> + +<p> + systemd implements its own credentials store mechanism, for no obvious +benefit. The whole credentials system needs to be reimplemented outside +of systemd in order for credentials-related directives to be supported +by s6. Consequently, all these directives are rated <strong>6</strong>. +</p> + +<h4 id="systemd.exec-sysv"> + System V compatibility +</h4> + +<p> + The utmp directives can be made significantly easier to implement if the target +system is using <a href="//skarnet.org/software/utmps/">utmps</a>, +because the directives then become a single call to +<a href="//skarnet.org/software/utmps/utmps-write.html">utmps-write</a> +with the relevant options. If <a href="//skarnet.org/software/utmps/">utmps</a> +cannot be used, then the utmp calls need to be reimplemented. +</p> + +<ul> + <li> <tt>UtmpIdentifier=</tt> : <strong>4</strong>. </li> + <p /> + <li> <tt>UtmpMode=</tt> : <strong>4</strong>. </li> +</ul> + +<h3 id="systemd.kill"> + Directives documented in <a href="https://man7.org/linux/man-pages/man5/systemd.kill.5.html">systemd.kill(5)</a> +</h3> + +<ul> + <li> <tt>KillMode=</tt> : depends on the kill mode. +<tt>control-group</tt> and <tt>mixed</tt> are <strong>3</strong>, +because they require cgroup control commands (that can be implemented +in shell). <tt>process</tt> is <strong>1</strong>. <tt>none</tt> is +<strong>2</strong>. </li> + <p /> + <li> <tt>KillSignal=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>RestartKillSignal=</tt> : <strong>5</strong>. s6 +doesn't use a different signal for restarting; implementing this +requires an outer layer. (This is overengineering.) </li> + <p /> + <li> <tt>SendSIGHUP=</tt> : <strong>5</strong>. Same. </li> + <p /> + <li> <tt>SendSIGKILL=</tt> : <strong>1</strong>. </li> + <p /> + <li> <tt>FinalKillSignal=</tt> : <strong>5</strong>. (This +is <em>absolute</em> overengineering.) </li> + <p /> + <li> <tt>WatchdogSignal=</tt> : <strong>7</strong>. Only meaningful +with an implementation of systemd's watchdog system. </li> +</ul> + +<h3 id="systemd.resource-control"> + Directives documented in <a href="https://man7.org/linux/man-pages/man5/systemd.resource-control.5.html">systemd.resource-control(5)</a> +</h3> + +<p> + All these directives relate to cgroups, so implementing them means +having access to at least some cgroups commands (difficulty at least +<strong>3</strong>. Others are even more involved, requiring tight +service integration with the system. Generally, seeing these directives +in your unit files is a bad sign; despite some of them only having +<strong>3</strong> or <strong>4</strong> listed, we do not recommend +implementing <a href="https://man7.org/linux/man-pages/man5/systemd.resource-control.5.html">systemd.resource-control(5)</a> +without having a full holistic view of the system. +</p> + +<ul> + <li> <tt>CPUAccounting=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>CPUWeight=</tt> : <strong>4</strong>. </li> + <p /> + <li> <tt>StartupCPUWeight=</tt> : <strong>9</strong>. Involves +startup and shutdown. </li> + <p /> + <li> <tt>CPUQuota=</tt> : <strong>4</strong>. </li> + <p /> + <li> <tt>CPUQuotaPeriodSec=</tt> : <strong>4</strong>. </li> + <p /> + <li> <tt>AllowedCPUs=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>StartupAllowedCPUs=</tt> : <strong>9</strong>. Involves +startup and shutdown. </li> + <p /> + <li> <tt>AllowedMemoryNodes=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>StartupAllowedMemoryNodes=</tt> : <strong>9</strong>. +Involves startup and shutdown. </li> + <p /> + <li> <tt>MemoryAccounting=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>MemoryMin=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>MemoryLow=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>MemoryHigh=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>MemoryMax=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>MemorySwapMax=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>MemoryZSwapMax=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>TasksAccounting=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>TasksMax=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>IOAccounting=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>IOWeight=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>StartupIOWeight=</tt> : <strong>9</strong>. Involves +startup and shutdown. </li> + <p /> + <li> <tt>IODeviceWeight=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>IOReadBandwidthMax=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>IOWriteBandwidthMax=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>IOReadIOPSMax=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>IOWriteIOPSMax=</tt> : <strong>5</strong>. </li> + <p /> + <li> <tt>IODeviceLatencyTargetSec=</tt> : <strong>4</strong>. </li> + <p /> + <li> <tt>IPAccounting=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>IPAddressAllow=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>IPAddressDeny=</tt> : <strong>7</strong>. </li> + <p /> + <li> <tt>IPIngressFilterPath=</tt> : <strong>8</strong>. </li> + <p /> + <li> <tt>IPEgressFilterPath=</tt> : <strong>8</strong>. </li> + <p /> + <li> <tt>BPFProgram=</tt> : <strong>8</strong>. </li> + <p /> + <li> <tt>SocketBindAllow=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>SocketBindDeny=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>RestrictNetworkInterfaces=</tt> : <strong>4</strong>. </li> + <p /> + <li> <tt>DeviceAllow=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>DevicePolicy=</tt> : <strong>6</strong>. </li> + <p /> + <li> <tt>Slice=</tt> : <strong>9</strong>. Slices are a systemd concept, +and fully implementing them requires a holistic system analysis. </li> + <p /> + <li> <tt>Delegate=</tt> : <strong>4</strong>. </li> + <p /> + <li> <tt>DisableControllers=</tt> : <strong>3</strong>. </li> + <p /> + <li> <tt>ManagedOOMSwap=</tt> : <strong>8</strong>. Out-of-memory +management is an entire systemd subsystem; instead of implementing that, +we recommend provisioning your machines correctly, and freeing up more +resources for your applications by using s6. + <p /> + <li> <tt>ManagedOOMMemoryPressure=</tt> : <strong>8</strong>. </li> + <p /> + <li> <tt>ManagedOOMMemoryPressureLimit=</tt> : <strong>8</strong>. </li> + <p /> + <li> <tt>ManagedOOMPreference=</tt> : <strong>8</strong>. </li> +</ul> + + +<h2 id="by-difficulty"> Directives rated by difficulty </h2> + +<p> + Use this section to answer the question: "If I were to write a converter tool +from systemd to s6, what subset of the unit file syntax should I focus on +first?" +</p> + +<p> + Take this classification with a grain of salt: for instance, it does not +make sense to implement an easy directive if it's only used in the context +of a larger subsystem that's much harder to implement - typically, most +cgroups-related resource control directives. +</p> + +<h3 id="difficulty-0"> + Difficulty: 0 — directives that can be ignored +</h3> + +<ul> + <li> <tt>Description=</tt> </li> + <li> <tt>Documentation=</tt> </li> + <li> <tt>Upholds=</tt> </li> + <li> <tt>PropagatesReloadTo=</tt> </li> + <li> <tt>PropagatesStopTp=</tt> </li> + <li> <tt>StopPropagatedFrom=</tt> </li> + <li> <tt>IgnoreOnIsolate=</tt> </li> + <li> <tt>StopWhenUnneeded=</tt> </li> + <li> <tt>AllowIsolate=</tt> </li> + <li> <tt>CollectMode=</tt> </li> + <li> <tt>SourcePath=</tt> </li> + <li> <tt>Type=idle</tt> </li> + <li> <tt>RemainAfterExit=</tt> </li> + <li> <tt>GuessMainPid=</tt> </li> + <li> <tt>ExecReload=</tt> </li> + <li> <tt>TimeoutStartFailureMode=</tt> </li> + <li> <tt>TimeoutStopFailureMode=</tt> </li> +</ul> + +<h3 id="difficulty-1"> + Difficulty: 1 — direct functionality mapping +</h3> + +<ul> + <li> <tt>RefuseManualStop=</tt> </li> + <li> <tt>FailureActionExitStatus=</tt> </li> + <li> <tt>SuccessActionExitStatus=</tt> </li> + <li> <tt>Type=simple</tt>, <tt>exec</tt> or <tt>oneshot</tt> </li> + <li> <tt>ExitType=main</tt> </li> + <li> <tt>TimeoutStartSec=</tt> </li> + <li> <tt>TimeoutStopSec=</tt> </li> + <li> <tt>TimeoutSec=</tt> </li> + <li> <tt>Restart=always</tt> </li> + <li> <tt>RestartPreventExitStatus=</tt> </li> + <li> <tt>NotifyAccess=none</tt> </li> + <li> <tt>ExecSearchPath=</tt> </li> + <li> <tt>RootDirectory=</tt> </li> + <li> <tt>SupplementaryGroups=</tt> </li> + <li> <tt>LimitCPU=</tt> </li> + <li> <tt>LimitFSIZE=</tt> </li> + <li> <tt>LimitDATA=</tt> </li> + <li> <tt>LimitSTACK=</tt> </li> + <li> <tt>LimitCORE=</tt> </li> + <li> <tt>LimitRSS=</tt> </li> + <li> <tt>LimitNOFILE=</tt> </li> + <li> <tt>LimitAS=</tt> </li> + <li> <tt>LimitNPROC=</tt> </li> + <li> <tt>LimitMEMLOCK=</tt> </li> + <li> <tt>UMask=</tt> </li> + <li> <tt>Nice=</tt> </li> + <li> <tt>RuntimeDirectory=</tt> </li> + <li> <tt>StateDirectory=</tt> </li> + <li> <tt>CacheDirectory=</tt> </li> + <li> <tt>LogsDirectory=</tt> </li> + <li> <tt>ConfigurationDirectory=</tt> </li> + <li> <tt>RuntimeDirectoryMode=</tt> </li> + <li> <tt>StateDirectoryMode=</tt> </li> + <li> <tt>CacheDirectoryMode=</tt> </li> + <li> <tt>LogsDirectoryMode=</tt> </li> + <li> <tt>ConfigurationDirectoryMode=</tt> </li> + <li> <tt>Environment=</tt> </li> + <li> <tt>EnvironmentFile=</tt> </li> + <li> <tt>PassEnvironment=</tt> </li> + <li> <tt>UnsetEnvironment=</tt> </li> + <li> <tt>StandardInput=</tt> </li> + <li> <tt>StandardOutput=</tt> (except <tt>journal</tt>) </li> + <li> <tt>StandardError=</tt> (except <tt>journal</tt>) </li> + <li> <tt>TTYPath=</tt> </li> + <li> <tt>KillMode=process</tt> </li> + <li> <tt>KillSignal=</tt> </li> + <li> <tt>SendSIGKILL=</tt> </li> +</ul> + +<h3 id="difficulty-2"> + Difficulty: 2 — straightforward implementation +</h3> + +<ul> + <li> <tt>Requires=</tt> </li> + <li> <tt>Before=</tt> </li> + <li> <tt>After=</tt> </li> + <li> <tt>OnSuccess=</tt> </li> + <li> <tt>DefaultDependencies=</tt> </li> + <li> <tt>Type=forking</tt> </li> + <li> <tt>PIDFile=</tt> </li> + <li> <tt>ExecStart=</tt> (omitting some prefixes) </li> + <li> <tt>ExecStartPre=</tt> </li> + <li> <tt>ExecStartPost=</tt> </li> + <li> <tt>ExecCondition=</tt> </li> + <li> <tt>ExecStopPost=</tt> </li> + <li> <tt>RestartSec=</tt> </li> + <li> <tt>Restart=</tt> except <tt>on-watchdog</tt> </li> + <li> <tt>RestartForceExitStatus=</tt> </li> + <li> <tt>RootDirectoryStartOnly=</tt> </li> + <li> <tt>WorkingDirectory=</tt> </li> + <li> <tt>LimitLOCKS=</tt> </li> + <li> <tt>LimitSIGPENDING=</tt> </li> + <li> <tt>LimitMSGQUEUE=</tt> </li> + <li> <tt>LimitNICE=</tt> </li> + <li> <tt>LimitRTPRIO=</tt> </li> + <li> <tt>LimitRTTIME=</tt> </li> + <li> <tt>OOMScoreAdjust=</tt> </li> + <li> <tt>IgnoreSIGPIPE=</tt> </li> + <li> <tt>StandardInputText=</tt> </li> + <li> <tt>StandardInputData=</tt> </li> + <li> <tt>SyslogIdentifier=</tt> </li> + <li> <tt>SyslogFacility=</tt> </li> + <li> <tt>SyslogLevel=</tt> </li> + <li> <tt>KillMode=none</tt> </li> +</ul> + +<h3 id="difficulty-3"> + Difficulty: 3 — requires easy additional programming +</h3> + +<ul> + <li> <tt>Wants=</tt> </li> + <li> <tt>Requisite=</tt> </li> + <li> <tt>BindsTo=</tt> </li> + <li> <tt>PartOf=</tt> </li> + <li> <tt>FailureAction=</tt> </li> + <li> <tt>SuccessAction=</tt> </li> + <li> <tt>StartLimitIntervalSec=</tt> </li> + <li> <tt>StartLimitBurst=</tt> </li> + <li> <tt>StartLimitAction=</tt> </li> + <li> <tt>ExitType=cgroup</tt> </li> + <li> <tt>SuccessExitStatus=</tt> </li> + <li> <tt>User=</tt> </li> + <li> <tt>Group=</tt> </li> + <li> <tt>Personality=</tt> </li> + <li> <tt>CPUSchedulingPolicy=</tt> </li> + <li> <tt>CPUSchedulingPriority=</tt> </li> + <li> <tt>CPUSchedulingResetOnFork=</tt> </li> + <li> <tt>CPUAffinity=</tt> </li> + <li> <tt>NUMAPolicy=</tt> </li> + <li> <tt>NUMAMask=</tt> </li> + <li> <tt>IOSchedulingClass=</tt> </li> + <li> <tt>IOSchedulingPriority=</tt> </li> + <li> <tt>RuntimeDirectoryPreserve=</tt> </li> + <li> <tt>TimeoutCleanSec=</tt> </li> + <li> <tt>LoglevelMax=</tt> </li> + <li> <tt>TTYReset=</tt> </li> + <li> <tt>TTYVHangup=</tt> </li> + <li> <tt>TTYRows=</tt> </li> + <li> <tt>TTYColumns=</tt> </li> + <li> <tt>TTYDisallocate=</tt> </li> + <li> <tt>KillMode=control-group</tt> and <tt>mixed</tt> </li> + <li> <tt>CPUAccounting=</tt> </li> + <li> <tt>AllowedCPUs=</tt> </li> + <li> <tt>AllowedMemoryNodes=</tt> </li> + <li> <tt>MemoryAccounting=</tt> </li> + <li> <tt>MemoryMin=</tt> </li> + <li> <tt>MemoryLow=</tt> </li> + <li> <tt>MemoryHigh=</tt> </li> + <li> <tt>MemoryMax=</tt> </li> + <li> <tt>MemorySwapMax=</tt> </li> + <li> <tt>MemoryZSwapMax=</tt> </li> + <li> <tt>TasksAccounting=</tt> </li> + <li> <tt>TasksMax=</tt> </li> + <li> <tt>IOAccounting=</tt> </li> + <li> <tt>IOWeight=</tt> </li> + <li> <tt>DisableControllers=</tt> </li> +</ul> + +<h3 id="difficulty-4"> + Difficulty: 4 — requires medium additional programming +</h3> + +<ul> + <li> <tt>RuntimeMaxSec=</tt> </li> + <li> <tt>RuntimeRandomizedExtraSec=</tt> </li> + <li> <tt>RequiresMountsFor=</tt> </li> + <li> <tt>RefuseManualStart=</tt> </li> + <li> <tt>PAMName=</tt> </li> + <li> <tt>CapabilityBoundingSet=</tt> </li> + <li> <tt>AmbientCapabilities=</tt> </li> + <li> <tt>NoNewPrivileges=</tt> </li> + <li> <tt>SecureBits=</tt> </li> + <li> <tt>CoredumpFilter=</tt> </li> + <li> <tt>TimerSlackNSec=</tt> </li> + <li> <tt>LogFilterPatterns=</tt> </li> + <li> <tt>SyslogLevelPrefix=</tt> </li> + <li> <tt>UtmpIdentifier=</tt> </li> + <li> <tt>UtmpMode=</tt> </li> + <li> <tt>CPUWeight=</tt> </li> + <li> <tt>CPUQuota=</tt> </li> + <li> <tt>CPUQuotaPeriodSec=</tt> </li> + <li> <tt>IODeviceLatencyTargetSec=</tt> </li> + <li> <tt>RestrictNetworkInterfaces=</tt> </li> + <li> <tt>Delegate=</tt> </li> +</ul> + +<h3 id="difficulty-5"> + Difficulty: 5 — requires complex additional programming +</h3> + +<ul> + <li> <tt>Conflicts=</tt> </li> + <li> <tt>OnFailure=</tt> </li> + <li> <tt>RebootArgument=</tt> </li> + <li> <tt>Type=dbus</tt> </li> + <li> <tt>BusName=</tt> </li> + <li> <tt>NonBlocking=</tt> </li> + <li> <tt>Sockets=</tt> </li> + <li> <tt>DynamicUser=</tt> </li> + <li> <tt>SELinuxContext=</tt> </li> + <li> <tt>AppArmorProfile=</tt> </li> + <li> <tt>SmackProcessLabel=</tt> </li> + <li> <tt>KeyringMode=</tt> </li> + <li> <tt>ReadWritePaths=</tt> </li> + <li> <tt>ReadOnlyPaths=</tt> </li> + <li> <tt>InaccessiblePaths=</tt> </li> + <li> <tt>ExecPaths=</tt> </li> + <li> <tt>NoExecPaths=</tt> </li> + <li> <tt>TemporaryFilesystem=</tt> </li> + <li> <tt>PrivateTmp=</tt> </li> + <li> <tt>PrivateDevices=</tt> </li> + <li> <tt>PrivateIPC=</tt> </li> + <li> <tt>IPCNamespacePath=</tt> </li> + <li> <tt>PrivateUsers=</tt> </li> + <li> <tt>ProtectHostname=</tt> </li> + <li> <tt>RemoveIPC=</tt> </li> + <li> <tt>PrivateMounts=</tt> </li> + <li> <tt>RestartKillSignal=</tt> </li> + <li> <tt>SendSIGHUP=</tt> </li> + <li> <tt>FinalKillSignal=</tt> </li> + <li> <tt>IODeviceWeight=</tt> </li> + <li> <tt>IOReadBandwidthMax=</tt> </li> + <li> <tt>IOWriteBandwidthMax=</tt> </li> + <li> <tt>IOReadIOPSMax=</tt> </li> + <li> <tt>IOWriteIOPSMax=</tt> </li> +</ul> + +<h3 id="difficulty-6"> + Difficulty: 6 — requires a full independent implementation +of a Linux subsystem and/or a part of the systemd architecture +</h3> + +<ul> + <li> <tt>OnFailureJobMode=</tt> </li> + <li> <tt>RootImage=</tt> </li> + <li> <tt>RootImageOptions=</tt> </li> + <li> <tt>MountAPIVFS=</tt> </li> + <li> <tt>ProtectProc=</tt> </li> + <li> <tt>ProcSubset=</tt> </li> + <li> <tt>BindPaths=</tt> </li> + <li> <tt>BindReadOnlyPaths=</tt> </li> + <li> <tt>MountImages=</tt> </li> + <li> <tt>ExtensionImages=</tt> </li> + <li> <tt>ExtensionDirectories=</tt> </li> + <li> <tt>ProtectSystem=</tt> </li> + <li> <tt>ProtectHome=</tt> </li> + <li> All <a href="https://man7.org/linux/man-pages/man5/systemd.exec.5.html#CREDENTIALS">credentials-related</a> directives </li> + <li> <tt>SocketBindAllow=</tt> </li> + <li> <tt>SocketBindDeny=</tt> </li> + <li> <tt>DeviceAllow=</tt> </li> + <li> <tt>DevicePolicy=</tt> </li> +</ul> + +<h3 id="difficulty-7"> + Difficulty: 7 — requires a full independent implementation +of a complex Linux subsystem and/or a significant part of the +systemd architecture +</h3> + +<ul> + <li> <tt>Type=notify</tt> </li> + <li> <tt>TimeoutAbortSec=</tt> </li> + <li> <tt>TimeoutStartFailureMode=abort</tt> </li> + <li> <tt>TimeoutStopFailureMode=abort</tt> </li> + <li> <tt>WatchdogSec=</tt> </li> + <li> <tt>Restart=on-watchdog</tt> </li> + <li> <tt>NotifyAccess=</tt> </li> + <li> <tt>FileDescriptorStoreMax=</tt> </li> + <li> <tt>ProtectClock=</tt> </li> + <li> <tt>ProtectKernelTunables=</tt> </li> + <li> <tt>ProtectKernelModules=</tt> </li> + <li> <tt>ProtectKernelLogs=</tt> </li> + <li> <tt>ProtectControlGroups=</tt> </li> + <li> <tt>RestrictAddressFamilies=</tt> </li> + <li> <tt>RestrictFilesystems=</tt> </li> + <li> <tt>RestrictNamespaces=</tt> </li> + <li> <tt>LockPersonality=</tt> </li> + <li> <tt>MemoryDenyWriteExecute=</tt> </li> + <li> <tt>RestrictRealtime=</tt> </li> + <li> <tt>RestrictSUIDSGID=</tt> </li> + <li> <tt>WatchdogSignal=</tt> </li> + <li> <tt>IPAccounting=</tt> </li> + <li> <tt>IPAddressAllow=</tt> </li> + <li> <tt>IPAddressDeny=</tt> </li> +</ul> + +<h3 id="difficulty-8"> + Difficulty: 8 — requires a complete implementation of complex +Linux-specific tooling +</h3> + +<ul> + <li> <tt>JoinsNamespaceOf=</tt> </li> + <li> <tt>PrivateNetwork=</tt> </li> + <li> <tt>NetworkNamespacePath=</tt> </li> + <li> <tt>SystemCallFilter=</tt> </li> + <li> <tt>SystemCallErrorNumber=</tt> </li> + <li> <tt>SystemCallArchitectures=</tt> </li> + <li> <tt>SystemCallLog=</tt> </li> + <li> <tt>IPIngressFilterPath=</tt> </li> + <li> <tt>IPEgressFilterPath=</tt> </li> + <li> <tt>BPFProgram=</tt> </li> + <li> <tt>ManagedOOMSwap=</tt> </li> + <li> <tt>ManagedOOMMemoryPressure=</tt> </li> + <li> <tt>ManagedOOMMemoryPressureLimit=</tt> </li> + <li> <tt>ManagedOOMPreference=</tt> </li> +</ul> + +<h3 id="difficulty-9"> + Difficulty: 9 — requires a full system analysis and remodelization +</h3> + +<ul> + <li> <tt>JobTimeoutSec=</tt> </li> + <li> <tt>JobRunningTimeoutSec=</tt> </li> + <li> <tt>JobTimeoutAction=</tt> </li> + <li> <tt>JobTimeoutRebootArgument=</tt> </li> + <li> Conditions and Asserts </li> + <li> <tt>USBFunctionDescriptors=</tt> </li> + <li> <tt>USBFunctionStrings=</tt> </li> + <li> <tt>OOMPolicy=</tt> </li> + <li> <tt>RootHash=</tt> </li> + <li> <tt>RootHashSignature=</tt> </li> + <li> <tt>RootVerity=</tt> </li> + <li> <tt>StartupCPUWeight=</tt> </li> + <li> <tt>StartupAllowedCPUs=</tt> </li> + <li> <tt>StartupAllowedMemoryNodes=</tt> </li> + <li> <tt>StartupIOWeight=</tt> </li> + <li> <tt>Slice=</tt> </li> +</ul> + +<h3 id="difficulty-10"> + Difficulty: 10 — implementing this basically means reimplementing systemd +</h3> + +<ul> + <li> <tt>StandardOutput=journal</tt> </li> + <li> <tt>StandardError=journal</tt> </li> + <li> <tt>LogExtraFields=</tt> </li> + <li> <tt>LogRateLimitIntervalSec=</tt> </li> + <li> <tt>LogRateLimitBurst=</tt> </li> + <li> <tt>LogNamespace=</tt> </li> +</ul> + +</body> +</html> |