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If a Linux service starts with systemctl start but is absent after a reboot, separate the problem into two questions: was the unit enabled so the boot transaction could pull it in, and if it was started, why did it fail? Run systemctl status and the current-boot journal first, then verify target membership, dependencies, and the service’s boot-time environment. This preserves the original evidence instead of guessing.
The procedure below applies to systemd-managed services. Replace UNIT.service with the actual unit name, and keep the command output before changing anything.
Start and enable are different operations
systemctl start UNIT.service starts a unit in the current boot only. It does not create the relationship that starts the unit on the next boot. systemctl enable UNIT.service installs the links declared by the unit’s [Install] section, usually under a target such as multi-user.target. Enabling changes future boot behavior but does not necessarily start the service in the current session.
| Command | What it changes | When to use it |
|---|---|---|
systemctl start UNIT.service |
Starts the unit now; the change is not a boot policy. | Testing a unit or starting it for the current boot. |
systemctl enable UNIT.service |
Creates the boot-time links described by [Install]. |
Making activation persistent across reboots. |
systemctl enable --now UNIT.service |
Enables the unit and starts it immediately. | When both persistent enablement and an immediate start are intended. |
systemctl disable UNIT.service |
Removes the enablement links; it does not necessarily stop a running process. | Preventing automatic activation on future boots. |
A unit can also be started indirectly by another unit’s dependency, socket activation, a timer, or a target. Therefore, “enabled” is not the only route to activation, but it is the usual route for a conventional boot service.
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Capture the failed boot before changing anything
First identify the exact unit name. Package documentation, systemctl list-unit-files, or the command that worked manually can reveal whether the name ends in .service. Then run this sequence as root or with sudo:
sudo systemctl status UNIT.servicesudo journalctl -u UNIT.service -b --no-pagersudo systemctl is-enabled UNIT.servicesudo systemctl is-active UNIT.servicesudo systemctl cat UNIT.servicesudo systemctl list-dependencies default.targetsudo systemd-analyze verify /etc/systemd/system/UNIT.servicesudo systemctl daemon-reloadsudo systemctl restart UNIT.service
systemctl status shows the loaded definition, active state, recent result, process identifier, and a short log tail. The unit-specific journal command restricts entries to this boot with -b; journalctl -b without -u shows the complete current-boot journal when you need surrounding dependency messages. Save the output before editing files so an overwritten configuration or a later restart does not erase the original failure context.
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What to look for in the evidence
- An exit status or signal reported by the service process.
- A missing executable, configuration file, directory, socket, mount, or secret.
- Permission or ownership errors, including inability to read a private key or write a log directory.
- A start timeout, stop timeout, or a process that never reaches its expected ready state.
- A dependency that failed, was skipped, or was not available when this unit ran.
- Messages emitted by the application itself; these are often more specific than systemd’s summary.
- A deliberate skip caused by a
Condition*orAssert*directive.
For a boot that appears stuck rather than failed, the systemd project recommends checking pending jobs with systemctl list-jobs. A job waiting on a mount, device, network unit, or another service can make the symptom look like a missing service.
Verify that boot actually pulls the unit in
Check enablement and the install declaration
Run systemctl is-enabled UNIT.service and inspect the definition with systemctl cat UNIT.service. The latter prints the vendor unit and any drop-ins that systemd has loaded. Look for an [Install] section containing a target relationship such as WantedBy=multi-user.target. If the unit has no install section, enable may have nothing to create; it may be intended to start only through another unit, a socket, or a timer.
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Do not assume that a successful manual start proves the unit is part of the boot transaction. The default boot target is the target systemd activates on boot. Target units primarily group other units through dependencies, so a service must be reachable from that target (directly or through another dependency) to be started as part of normal boot.
Inspect the target’s dependency graph
Use systemctl list-dependencies default.target to see what the active default target wants or requires. If your machine uses a different default target, resolve it with systemctl get-default and inspect that target instead. A unit that is enabled for a target you never boot will not appear in the transaction you expect.
When a unit was edited, renamed, or moved, the old enablement links can point at the previous declaration. After validating the new file and reloading systemd, run sudo systemctl reenable UNIT.service. This removes and recreates the links from the current [Install] section.
Compare the boot environment with your login shell
A command that works in an interactive shell often relies on state that systemd does not provide: a home-directory working directory, a customized PATH, shell aliases, exported variables, mounted filesystems, credentials, or an agent socket. Make the service’s requirements explicit instead of copying a long login environment into the unit.
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Executable paths and permissions
- Use an absolute path in
ExecStart=, such as/usr/local/bin/exampled, rather than relying on shell lookup. - Confirm the file exists and is executable, and that every parent directory is searchable by the configured service user.
- If
User=appuseris set, test access as that account. A root shell test can conceal permission failures. - Remember that systemd does not interpret shell syntax in
ExecStart=the way an interactive shell does. If pipelines, redirection, or variable expansion are required, invoke a shell explicitly and understand the security trade-off.
Working directory and configuration files
Set WorkingDirectory= when the program expects relative paths. Prefer absolute configuration paths in the command line or the application’s documented option. Verify that the configuration file exists at boot and is readable by the service user; a path under a user-mounted directory may not exist when a system service starts.
Environment variables and credentials
Variables present in your terminal are not automatically present in a system service. Define required values with Environment= or an appropriately protected EnvironmentFile=, or use the application’s native credentials mechanism. Avoid putting passwords directly in a world-readable unit file. Confirm the variable names and file permissions in the journal when the program reports an incomplete configuration.
Sockets, mounts, and other resources
Check that required sockets, device nodes, network addresses, and mount points exist at the time the service starts. If a database socket is created by another unit, express that relationship rather than relying on an arbitrary sleep. For a filesystem, ensure the corresponding mount unit is available and ordered before the service. A path that is present later in the boot may explain why a manual start succeeds.
Separate dependency from ordering
Unit relationships have two independent parts. Wants= or Requires= pulls another unit into the transaction; After= and Before= determine order. One does not automatically imply the other.
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| Directive | Effect | Typical diagnostic question |
|---|---|---|
Wants= |
Requests another unit as part of the transaction, without making this unit fail solely because the wanted unit fails. | Was the supporting unit pulled in at all? |
Requires= |
Expresses a stronger dependency; failure or disappearance of the required unit can affect this unit. | Did the required unit fail and take this service down? |
After= |
Starts this unit after the named unit when both are in the same transaction. | Was the prerequisite ready before this process accessed it? |
Before= |
Places this unit before the named unit in ordering. | Is another unit incorrectly racing ahead? |
Add a specific ordering relationship only when the dependency really must be ready first. An After=network-online.target line, for example, changes ordering but does not itself pull the network target into the transaction. Pair dependency and ordering deliberately, and avoid broad changes to the default target when a unit-local drop-in is sufficient.
Find races and slow jobs
systemd-analyze blamelists jobs by elapsed startup time and can reveal a timeout or unexpectedly slow prerequisite.systemd-analyze critical-chainshows the ordered path that delayed the boot target.systemd-analyze plot > boot.svgcreates a timeline you can open in a browser to see overlap, gaps, and late-starting units.
Use these tools with the journal. A slow unit is not necessarily the failed unit; it may expose the mount, DNS, device, or dependency that caused the service to time out.
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Make the smallest change that addresses the observed error. A drop-in is usually safer than editing a package-owned unit:
sudo systemctl edit UNIT.serviceFor a unit file stored in /etc/systemd/system/, validate its syntax and referenced settings with:
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sudo systemd-analyze verify /etc/systemd/system/UNIT.serviceUse the distribution’s equivalent path if the file lives elsewhere. Then make systemd reread unit files and retest:
sudo systemctl daemon-reloadsudo systemctl restart UNIT.servicesudo systemctl status UNIT.servicesudo journalctl -u UNIT.service -b --no-pager
daemon-reload is required after changing a unit or drop-in; restarting alone does not make the manager read a new definition. If you changed the [Install] section, follow the reload with sudo systemctl reenable UNIT.service so the symlinks match the new declaration.
Common corrective edits
- Replace a relative
ExecStartpath with an absolute executable path. - Add the missing
WorkingDirectoryor configuration path. - Correct
User=, group membership, file ownership, or directory permissions. - Add a narrowly scoped
Wants=/Requires=and matchingAfter=relationship for a real prerequisite. - Adjust
TimeoutStartSec=only when the application legitimately needs more time; do not hide a dependency failure with an arbitrarily large timeout. - Review
Condition*andAssert*directives when the journal says the unit was skipped rather than failed.
Classify the failure before choosing a fix
| Failure class | Evidence | Focused response |
|---|---|---|
| Disabled or not pulled in | is-enabled does not show the intended relationship, or the unit is absent from the default target’s dependencies. |
Inspect [Install], enable or reenable the unit, and confirm the correct default target. |
| Dependency or ordering | Journal entries show a failed prerequisite, a missing mount, or a process starting before its resource exists. | Fix the prerequisite and add only the necessary dependency and ordering declarations. |
| Environment or permissions | The program reports an inaccessible file, directory, variable, socket, or credential; manual launch works under a different account. | Make paths, user identity, working directory, variables, and permissions explicit. |
| Executable or configuration error | Immediate nonzero exit, missing binary, invalid option, or parse error appears in status or the journal. | Correct the command or configuration, run systemd-analyze verify, reload, and restart. |
| Timeout | The unit remains in a starting state until systemd reports a start timeout. | Use critical-chain and the journal to find the slow prerequisite; increase the timeout only for a known legitimate startup duration. |
| Deliberate condition or assertion skip | The journal says a Condition* or Assert* test was not met. |
Provide the required condition or revise the directive only if skipping is not intended. |
Recover when the service blocks the machine’s boot
If a broken unit or mount prevents a normal login, use the boot loader’s kernel command line to select a recovery target. systemd.unit=rescue.target provides a fuller single-user recovery environment with basic services. systemd.unit=emergency.target provides a minimal shell for cases where more of the system cannot be brought up.
Emergency-mode procedure
- At the boot loader, append
systemd.unit=emergency.targetto the kernel command line and boot. - In the emergency shell, remount the root filesystem read-write before editing:
mount -o remount,rw /. - Inspect the unit, its drop-ins, the journal, and
/etc/fstabif a mount is involved. - Repair the smallest incorrect setting, or temporarily mask or disable the offending unit if that is necessary to regain a normal boot.
- Run
systemctl daemon-reloadafter changing unit files or/etc/fstab-related data. - Remove the temporary kernel option and any temporary debug shell or override before the next normal boot.
Rescue and emergency targets are recovery tools, not permanent operating modes. Record what you changed so you can restore the intended dependency and security settings after confirming a successful boot.
Verify the repair across a clean reboot
A successful manual restart proves only that the current environment works. Finish with a clean reboot and repeat the checks against the new boot:
- Confirm enablement:
sudo systemctl is-enabled UNIT.service. - Reboot normally.
- Check the resulting state:
sudo systemctl is-active UNIT.serviceandsudo systemctl status UNIT.service. - Read only the new boot’s records:
sudo journalctl -u UNIT.service -b --no-pager. - If it failed again, compare the first failing timestamp with
systemd-analyze critical-chainand inspect the prerequisite named in the journal.
Keep the fix local to the unit whenever possible, and document why each dependency, ordering rule, user, path, and timeout exists. That makes the next boot failure diagnosable instead of turning a one-line workaround into an opaque change to the whole startup graph.
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