https://github.com/msantos/pseudocron
sleep(1) using a cron expression
https://github.com/msantos/pseudocron
capsicum cron pledge seccomp
Last synced: 4 months ago
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sleep(1) using a cron expression
- Host: GitHub
- URL: https://github.com/msantos/pseudocron
- Owner: msantos
- License: apache-2.0
- Created: 2018-01-28T16:03:20.000Z (over 7 years ago)
- Default Branch: master
- Last Pushed: 2025-02-12T12:43:56.000Z (4 months ago)
- Last Synced: 2025-02-12T13:55:33.260Z (4 months ago)
- Topics: capsicum, cron, pledge, seccomp
- Language: C
- Homepage:
- Size: 49.8 KB
- Stars: 3
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE
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README
# SYNOPSIS
pseudocron [-n|-p|-v] *crontab expression*
# DESCRIPTION
pseudocron: sleep(1) using a cron expression
Also see [runcron](https://github.com/msantos/runcron).
cron expressions are parsed using
[ccronexpr](https://github.com/staticlibs/ccronexpr).
* simple
pseudocron is sleep(1) that accepts a crontab(5) expression for the
duration and then exits. That's all it does.
Use a supervisor like [daemontools](https://cr.yp.to/daemontools.html)
to run the job.
* safe
No setuid binaries or processes running as root.
pseudocron operations are restricted. It cannot open files
or sockets or signal processes. The only ways pseudocron can
interact with other processes is via stdin/stdout/stderr and
the process exit value.
* container friendly
pseudocron runs as a normal user without any special privileges.
It does not need to modify the filesystem. pseudocron is meant to
run in an automated environment without user intervention.
Since processes run sequentially and synchronously, jobs won't pile
up if the run time of the task exceeds the time spec increment unless
specifically requested to run in the background.
pseudocron does not modify the application environment or interfere
with stdio.
The standard crontab(5) expressions are supported. The seconds field
is optional:
```
field allowed values
----- --------------
second 0-59 (optional)
minute 0-59
hour 0-23
day of month 1-31
month 1-12 (or names, see below)
day of week 0-7 (0 or 7 is Sun, or use names)
```
crontab(5) aliases also work:
```
string meaning
------ -------
@reboot Run once, at startup (see below).
@yearly Run once a year, "0 0 1 1 *".
@annually (same as @yearly)
@monthly Run once a month, "0 0 1 * *".
@weekly Run once a week, "0 0 * * 0".
@daily Run once a day, "0 0 * * *".
@midnight (same as @daily)
@hourly Run once an hour, "0 * * * *".
@never Never run (sleep forever)
```
## @reboot
Unlike *crontab*(5), `pseudocron` will run the `@reboot` alias
immediately.
The behaviour can be mimicked by setting the `PSEUDOCRON_REBOOT`
environment variable. If the variable is unset, `@reboot` is equivalent to
`* * * * * *`.
If set to any value, `@reboot` is equivalent to `@never`.
```shell
#!/bin/sh
while :; do
# runs in the next second
pseudocron "@reboot"
echo test
export PSEUDOCRON_REBOOT=1
# equivalent to sleep infinity
done
```
# EXAMPLES
```
# parse only the crontab expression
# every 15 minutes (5 fields)
pseudocron -n "*/15 * * * *"
# parse only the crontab expression and view the calculated times
# every 15 seconds (6 fields)
pseudocron -nvv "*/15 * * * * *"
```
Writing a batch job:
```
#!/bin/sh
set -e
# Run daily at 8:15am
pseudocron "15 8 * * *"
echo Running job
```
# OPTIONS
-n, --dryrun
: Do not sleep. Can be used to verify the crontab expression.
-p, --print
: Output the number of seconds to the next crontab time specification.
-v, --verbose
: Output the calculated dates to stderr.
-h, --help
: display usage
--timestamp *YY*-*MM*-*DD* *hh*-*mm*-*ss*|*@seconds*
: Use *timestamp* for the initial start time instead of now.
--stdin
: Read crontab expression from stdin.
# BUILDING
## Quick Install
```
make
```
## Selecting a Sandbox
```
RESTRICT_PROCESS=null make clean all
```
## Using musl libc
```
## Using the rlimit mode process restriction
RESTRICT_PROCESS=rlimit ./musl-make
## linux seccomp mode process restriction: requires kernel headers
# clone the kernel headers somewhere
cd /path/to/dir
git clone https://github.com/sabotage-linux/kernel-headers.git
# then compile
PSEUDOCRON_INCLUDE=/path/to/dir ./musl-make clean all
```
## Sandbox
Setting the `RESTRICT_PROCESS` environment variable controls which
mode of process restriction is used. The available modes are:
* seccomp: linux
* pledge: openbsd
* capsicum: freebsd
* rlimit: all
* null: all
For example, to force using the rlimit process restriction:
```
RESTRICT_PROCESS=rlimit make clean all
```
The `null` mode disables process restrictions and can be used for debugging.
```
RESTRICT_PROCESS=null make clean all
strace -o null.trace ./pseudcron ...
RESTRICT_PROCESS=seccomp make clean all
strace -o seccomp.trace ./pseudcron ...
```
# ALTERNATIVES
* [runcron](https://github.com/msantos/runcron)
* [runwhen](http://code.dogmap.org/runwhen/)
* [supercronic](https://github.com/aptible/supercronic)
* [uschedule](https://ohse.de/uwe/uschedule.html)
# SEE ALSO
*crontab*(5), *sleep*(1)