Expected cron daemon behavior change from SLES11 to SLES12

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Environment

SUSE Linux Enterprise Server 11 (SLES11)
SUSE Linux Enterprise Server 12 (SLES12)
SUSE Linux Enterprise Server 15 (SLES15)

Situation

Attempting to start multiple instances of cron sometimes results in a Resource temporarily unavailable message.

SLES11 only allows one instance of cron (background process) or cron -n (foreground process).

sles11sp4:~ # ps aux | grep cron
root      3341  0.0  0.0  14808   672 ?        Ss   09:11   0:00 /usr/sbin/cron

sles11sp4:~ # cron
cron: can't lock /var/run/cron.pid, otherpid may be 3341: Resource temporarily unavailable

sles11sp4:~ # cron -n
cron: can't lock /var/run/cron.pid, otherpid may be 3341: Resource temporarily unavailable

sles11sp4:~ # ps aux | grep cron
root      3341  0.0  0.0  14808   672 ?        Ss   09:11   0:00 /usr/sbin/cron

SLES12 allows multiple instances of either cron (background) or cron -n (foreground).

sles12sp3:~ # ps aux | grep cron
root      1168  0.0  0.3  18880  2620 ?        Ss   09:40   0:00 /usr/sbin/cron -n

sles12sp3:~ # cron
sles12sp3:~ # cron
sles12sp3:~ # cron -n &
sles12sp3:~ # cron -n &

sles12sp3:~ # ps aux | grep cron
root      1168  0.0  0.3  18880  2620 ?        Ss   09:40   0:00 /usr/sbin/cron -n
root      1269  0.0  0.2  20136  1940 ?        Ss   09:42   0:00 cron
root      1271  0.0  0.2  20136  1940 ?        Ss   09:42   0:00 cron
root      1272  0.0  0.3  20140  2952 pts/0    S    09:42   0:00 cron -n
root      1273  0.0  0.3  20144  2888 pts/0    S    09:42   0:00 cron -n

Resolution

Kindly open a Service Request via SCC and ask for Program Temporary Fix "PTF" ; Fix is available and will be released in future cronie package.

Cause

SLES12 & SLES15 introduced a defect allowing multiple background and foreground instances of cron to run concurrently.

Additional Information

The expected behavior changed from SLES11 to SLE12 and beyond. The expected behavior is:

SLES11: Only one instance of cron (background) or cron -n (foreground) is allowed. All additional instances will result in resource temporarily unavailable.

SLES12 and SLES15: Only one instance of cron (background) is allowed, but multiple instances of cron -n (foreground) are allowed. All additional instances of cron (background) will result in resource temporarily unavailable. However, multiple instances of cron -n (foreground) are allowed and do not result in a resource restriction.

With new PTF SLES12 and SLES15 behaviour will be like SLES11 ; which means only one cron daemon is running, resulting in jobs not being executed multiple times.

Maintenance updates newer that cron-4.2-59.3.2 and cronie-1.4.11-59.3.2 are planned to include the PTF's fix as well.

Note: It is expected that only SLES12SP4 and SLES15 and their successors get the fixed packages. SLES versions and Service Packs proir do not get the fix automatically, but only upon request from customers with valid LTSS (Long Term Service Pack Support) entitlements.

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