Import vixie cron 4.0

Specifically, import the diff from commit e745bd4c10ab to
commit 83563783cc2 in https://github.com/vixie/cron.git

My sole motivation is changing to the common MIT license.
The

Import vixie cron 4.0

Specifically, import the diff from commit e745bd4c10ab to
commit 83563783cc2 in https://github.com/vixie/cron.git

My sole motivation is changing to the common MIT license.
The old license, especially the "buildable source" clause,
is unfriendly for commercial users of this code. Simply
changing the license without importing [most of] the code
accompanying that license seemed legally dubious.

The most regrettable change is losing Paul's uucp path.
I partially atone for this loss by restoring the upstream
$Id$ tags, since $FreeBSD$ is no longer useful.

This is [intended to be] a complete list of the functional
changes in this commit. Some changes were made so that we
could consider vixie cron to be our upstream and reduce our
diffs against it, while others were simply a good idea.

- main() - use putenv instead of setenv for PATH
- open_pidfile no longer needs snprintf to build pidfile
- crontab main() - abort() on impossible errors
- check for truncation when building strings with snprintf
- getdtablesize() -> sysconf(_SC_OPEN_MAX)

These changes were not taken from upstream's 4.0 diff because
they [could] actually change behavior. Some of them might be
beneficial, but should be taken separately.

- config.h - sendmail args: remove -oi and add -or0s
- call setlocale(LC_ALL, "") at the top of main()
- acquire_daemonlock - we already use pidfile
- cast getpid(), uid_t, and gid_t to long for printf
- remove unnecessary braces - I consider them beneficial
- BSDi support
- glue_strings() - use snprintf(), as we often already did

MFC after: on demand
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D40260

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cron: Use C89 function definitions.

Reviewed by: zlei
Differential Revision: https://reviews.freebsd.org/D39529

Add new functionality and syntax to cron(1) to allow to run jobs at a
given interval, which is counted in seconds since exit of the previous
invocation of the job. Example user crontab entry:

@25 sl

Add new functionality and syntax to cron(1) to allow to run jobs at a
given interval, which is counted in seconds since exit of the previous
invocation of the job. Example user crontab entry:

@25 sleep 10

The example will launch 'sleep 10' every 35 seconds. This is a rather
useless example above, but clearly explains the functionality.

The practical goal here is to avoid overlap of previous job invocation
to a new one, or to avoid too short interval(s) for jobs that last long
and doesn't have any point of immediate launch soon after previous run.

Another useful effect of interval jobs can be noticed when a cluster of
machines periodically communicates with a single node. Running the task
time based creates too much load on the node. Running interval based
spreads invocations across machines in cluster. Note that -j/-J won't
help in this case.

Sponsored by: Netflix

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MFhead@r320180

Merge ^/head r319973 through 321382.

Merge ^/head r320994 through r321238.

Fix trivial whitespace bug introduced in usage message changes for -n
support (r304570).

MFC after: now

MFhead @ r304815

Merge ^/head r304537 through r304699.

Add the "-n" flag to cron(8), to prevent it from daemonizing.
This makes it possible to use it with external supervisors.
The "-n" flag name is compatible with Linux, NetBSD, and OpenBSD.

Reviewed b

Add the "-n" flag to cron(8), to prevent it from daemonizing.
This makes it possible to use it with external supervisors.
The "-n" flag name is compatible with Linux, NetBSD, and OpenBSD.

Reviewed by: jilles, pfg, wblock
MFC after: 1 month
Differential Revision: https://reviews.freebsd.org/D7581

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usr.sbin: minor spelling fixes on comments.

No functional change.

MFC @ r266724

An SVM update will follow this.

Merge head

IFC @264767

MFH: tracking commit

Sponsored by: The FreeBSD Foundation

Merge head up to r262222 (last merge was incomplete).

MFH@261151.

Bad timespec_subtract() calculations produce negative tv_nsec on i386
which cause EINVAL returned from nanosleep() which cause loop in
cron_sleep() and making all cron jobs to start about 30 seconds

Bad timespec_subtract() calculations produce negative tv_nsec on i386
which cause EINVAL returned from nanosleep() which cause loop in
cron_sleep() and making all cron jobs to start about 30 seconds earlier
(which cause f.e. logfiles rotation by newsyslog delayed by 1 hour).

Use simple and proved calculations from kernel's timespecsub() instead.

MFC after: 3 days

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Merge fresh head.

MFC

MFC @ r241285

IFC @ r242684

Sync from head

Second attempt to add @every_second keyword support. Due to multiple
requests, default to the previous 60-seconds scheduling method
unless there is any @every_second entries to conserve CPU cycles an

Second attempt to add @every_second keyword support. Due to multiple
requests, default to the previous 60-seconds scheduling method
unless there is any @every_second entries to conserve CPU cycles and
power.

This change also improves scheduling in the default mode by running
as close to the beginning of the minnute as possible by replacing
sleep(3) with nanosleep(2). Previously, the tasks would run anywhere
within the first second of the minute and that offset drifted back
and forth each time cron(8) was engaged.

MFC after: 1 month

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Fully backout latest changes.

Pointy hat to: sobomax