Linux has no single, system-wide time when /tmp is cleared. On systems using the documented systemd defaults, systemd-tmpfiles removes files from /tmp when they reach an age of 10 days. The corresponding default for /var/tmp is 30 days. Cleanup is normally run by systemd-tmpfiles-clean.service, triggered by systemd-tmpfiles-clean.timer. A reboot may remove files on some systems, but it is neither the universal trigger nor a reliable schedule.
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The short answer: age-based cleanup, not a Linux-wide clock
The answer to “When does Linux clear /tmp?” depends on the distribution, the init system, the mount used for /tmp, and local administrator rules. There is no rule that every Linux machine empties the directory at shutdown, at boot, or at a particular time of day.
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On a host using the upstream systemd policy, files in /tmp are cleaned after they have reached 10 days of age. Files in /var/tmp have a 30-day default. Those numbers are maximum ages in the cleanup policy, not promises that deletion occurs exactly at the instant the limit is reached. The timer must run, and the file must match an applicable rule.
The policy is implemented by systemd-tmpfiles. Its cleanup operation evaluates the age parameters in tmpfiles.d rules and removes files and directories that qualify. The normal service and timer provide the recurring execution.
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What actually performs the cleanup
systemd-tmpfiles-clean.timer schedules the work
The timer starts systemd-tmpfiles-clean.service. The service invokes systemd-tmpfiles to apply the configured age rules across the system. Because the timer is a system unit, it can clean directories for all users, not just the account that created a file.
The timer’s exact calendar and any delay should be checked on the machine rather than assumed. A file that is 10 days old can remain until the next successful cleanup run, while a local rule can make the effective age shorter or longer.
tmpfiles.d supplies the rules
systemd-tmpfiles reads configuration from the installed system’s tmpfiles.d search path. The usual locations are:
/etc/tmpfiles.d/for administrator-created overrides and site policy./run/tmpfiles.d/for run-time-generated policy./usr/lib/tmpfiles.d/for rules supplied by installed packages.
Administrator rules in /etc/tmpfiles.d/ take precedence according to the system’s configuration lookup rules. A local rule can alter the age, exclude a path, create a directory, or request removal during an early-boot pass. Consequently, the upstream 10-day value is a useful baseline, not proof of what a particular host will do.
Does Linux delete /tmp on reboot?
Sometimes, but not universally. Two separate mechanisms are often confused:
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- Age-based cleanup: the systemd timer removes entries that satisfy their configured age. This can happen while the system is running, without a reboot.
- Filesystem lifecycle: if
/tmpis mounted as a volatiletmpfs, its contents normally exist only while that filesystem instance exists. Unmounting it, including during a shutdown, discards its contents.
A persistent filesystem mounted at /tmp can retain files across a reboot if no boot-time rule or age-based cleanup removes them. Conversely, a volatile mount can lose them even when their age is only a few seconds. The mount type and boot configuration therefore matter as much as the directory name.
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Some tmpfiles.d rules are intended for the early-boot operation. The systemd-tmpfiles --boot mode applies those rules. A distribution may use such rules to remove selected entries when boot starts, independently of the recurring clean timer.
How to find the policy on your machine
Use the following checks before relying on a temporary file for a job, build, socket, lock, or hand-off between processes.
- Check the timer state and next run. Run
systemctl status systemd-tmpfiles-clean.timer. This shows whether the timer is enabled and active. Then runsystemctl list-timers systemd-tmpfiles-clean.timerto see the last and next scheduled activation. - Check the cleanup service. Run
systemctl status systemd-tmpfiles-clean.service. A failed, masked, or repeatedly failing service explains why old entries remain or why cleanup is not happening as expected. - Read the effective rules. Inspect matching files under
/etc/tmpfiles.d/,/run/tmpfiles.d/, and/usr/lib/tmpfiles.d/. Search for rules covering/tmp,/var/tmp, or a parent path. Read the installedtmpfiles.dmanual for the rule type and age-field syntax used by that release. - Check the mount. Use
findmnt /tmp(or the system’s equivalent mount inspection command) to determine whether/tmpis a normal persistent filesystem or atmpfs. A volatile mount changes the answer after reboot or unmount. - Review recent service logs. Use
journalctl -u systemd-tmpfiles-clean.serviceto see cleanup runs and reported errors. Logs can distinguish a successful deletion pass from a timer that never activated.
These checks provide a machine-specific answer: which policy applies, when it last ran, when it is expected to run again, and whether the directory itself is volatile.
What the 10-day and 30-day defaults mean
| Path | Documented upstream systemd default age | What controls deletion |
|---|---|---|
/tmp |
10 days | Applicable tmpfiles.d age rule and a successful systemd-tmpfiles cleanup run |
/var/tmp |
30 days | Applicable tmpfiles.d age rule and a successful systemd-tmpfiles cleanup run |
The defaults describe file age, not a fixed deletion timestamp. A file’s relevant timestamps and the rule’s semantics determine whether it qualifies. Cleanup can also be constrained by permissions, mount state, locks, or other filesystem conditions. Never treat “10 days” as a retention guarantee for important data.
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Why a file in /tmp disappeared
It crossed the configured age threshold
The most common explanation is that a timer run found the file old enough under the active rule. A local administrator may have configured an age shorter than the upstream default, so inspect the effective files instead of assuming 10 days.
The machine rebooted or the mount was recreated
If /tmp is a volatile tmpfs, rebooting, changing mounts, or otherwise recreating that filesystem removes its contents. This loss is a property of the mount lifecycle, not evidence that the 10-day timer ran.
An early-boot rule removed it
A rule marked for boot-time processing can delete or recreate entries during startup. This is especially relevant when a file survives normal runtime but vanishes after a restart.
Another program removed it
Applications, package managers, service supervisors, installers, and user cleanup scripts can remove files in /tmp. If the systemd service log shows no relevant deletion and the mount is persistent, audit the application and user-level jobs that write there.
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Containers, chroots, sandboxes, and per-service namespaces can expose a different /tmp from the host. Check the path from the same execution context as the process that created the file. A host inspection may not show a container’s temporary directory, and vice versa.
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How to run or test cleanup safely
systemd-tmpfiles --clean applies the configured age-based cleanup rules. Running it manually can remove every matching entry system-wide, so use it only when you understand the active policy and have administrative authorization. Read the installed manual for preview or dry-run options available on that system before performing a destructive test.
After changing a rule, restart systemd-tmpfiles-clean.service so safe runtime changes are applied to the service. Also verify the timer and inspect the journal. A syntax error, wrong path, or override with higher precedence can make a seemingly correct change ineffective.
How to keep data that must survive cleanup
Use a persistent application directory
Do not store durable output, queued work, credentials, caches that must be retained, or user documents in /tmp. Place them in an application-specific directory on a persistent filesystem, with ownership and permissions appropriate to the service. Use /var/tmp only when the data is genuinely temporary but needs a longer default lifetime; it is still subject to policy and is not a backup location.
Create an intentional policy exception
If a temporary path must remain longer, add a documented tmpfiles.d rule or exclusion through the supported configuration mechanism for the distribution. Put administrator policy in /etc/tmpfiles.d/, verify that it overrides the packaged rule as intended, and test the result with the installed systemd-tmpfiles documentation. Keep the exception narrow: exempting all of /tmp defeats its purpose and can allow unbounded disk consumption.
Design for disappearance anyway
Even an exemption does not protect against a volatile mount, manual deletion, filesystem repair, container teardown, or an application restart that recreates its workspace. A robust program treats /tmp as disposable, recreates missing directories, writes atomically, and stores any irreplaceable state elsewhere.
Distribution and host differences
Modern systemd-based distributions commonly use the service-and-timer model, but not every Linux installation has the same implementation. Older systems or systems using a different init setup may rely on legacy boot scripts, cron jobs, or distribution-specific temporary-file cleaners. Their retention periods and run schedules can differ from the upstream systemd values.
Debian 13 release guidance explicitly warns that new installations regularly delete old files in both /tmp and /var/tmp while the system is running. That warning is important because it rules out a common assumption: waiting for a reboot is not necessary for cleanup on that release. The same principle applies to any distribution that schedules recurring cleanup.
When comparing machines, compare the mechanism, age threshold, timer cadence, boot-time rules, mount type, and local overrides. Comparing distribution names alone cannot predict when an individual file will disappear.
A practical decision guide
- Need a file for minutes or hours:
/tmpis appropriate, provided the program can recreate it. - Need temporary data across reboots: use a persistent application directory and define its own retention policy; do not rely on
/tmp. - Need a temporary file for more than 10 days: inspect the active rule first. The upstream default will not provide that retention in
/tmp. - Need to diagnose an unexpected deletion: check the timer, service journal, effective
tmpfiles.dfiles, mount type, boot events, and application logs in that order. - Need to change retention: make a narrow administrator override, validate its precedence and syntax, restart the cleanup service when appropriate, and monitor disk usage.
Bottom line for “How long do files stay in /tmp?”
On an unmodified systemd installation, the documented policy is 10 days for /tmp and 30 days for /var/tmp, enforced by recurring systemd-tmpfiles cleanup. Those are defaults, not universal guarantees. A volatile /tmp mount can empty at reboot, boot-time rules can remove entries during startup, and administrator or distribution-specific configuration can change every threshold. Check the timer, rules, service logs, and mount on the machine whose files matter.
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