busybox ntpd can not run as a time server

Package Information

• Package name: busybox
• Package version: 1.36.1-r29
• Alpine version: 3.20.3
• Alpine architecture: x86_64

Summary

The ntpd command can not be used as a time server. The conf.d comment says that adding -l to the options should enable this functionality. However ntpd crashes when that option is turned on.

ntpd would have reported permission denied, but since stderr/stdout is send to /dev/null nothing is shown.

This is caused by commit bcb45e25 which introduced a rootless ntpd. The commit changes the running user to ntp while adding the ^cap_sys_time capability. This is enough to change the time, but it is not enough to open the time server listening port. For that, the capability ^cap_net_bind_service also needs to be added. Adding this to the capabilities in the init scripts fixes this issue.

Steps to reproduce

• Add -l to the NTPD_OPTS in /etc/conf.d/ntpd.
• Restart ntpd: service ntpd restart
• Check if ntpd is running: service ntpd status
• It should show ntpd is running, but it actually shows ntpd is crashed.