Is "-s loglevel" option ignored when olcLogLevel is set while "-d" overwrites

The number of debug-level of '-d' command line option and syslog-level of '-s' command line option in slapd have the same meaning as we can confirm by:

$ slapd -d '?'
$ slapd -s '?'

The only difference between '-d' and '-s' is that '-d' is for foreground debug and '-s' is background logging level, I think.

Confirm "-d" debug-level

Even when slapd is running under olcLogLevel: 0:

$ sudo grep olcLogLevel /etc/openldap/slapd.d/cn=config.ldif
olcLogLevel: 0

slapd -d runs to overwrite olcLogLevel setting as I expect:

$ sudo systemctl stop slapd   # to avoid port conflict
$ sudo slapd -d 256           # run slapd with loglevel 256 in foreground (*a)

do ldapsearch in another terminal:

$ ldapsearch -x -H ldap://localhost -b dc=... -s base
...

(*a) shows loglevel=256 logs as I expect:

61b552f9 slapd starting
61b55313 conn=1000 fd=15 ACCEPT from IP=[::1]:40918 (IP=[::]:389)
...
61b55313 conn=1000 fd=15 closed

I can confirm -d -1 (all logging) works as well:

(stop (*a) slapd by ctrl-c)
$ sudo slapd -d -1
...
(a lot of logs)

while ldapsearch in another terminal:

$ ldapsearch -x -H ldap://localhost -b dc=... -s base
...

Confirm "-s syslog-level"

kill 'slapd -d' I started at (*a) and start slapd with -s 256 in background:

(stop (*a) slapd by ctrl-c)
$ sudo cat /etc/sysconfig/slapd
...
SLAPD_OPTIONS="-s 256"

$ sudo systemctl start slapd

I can confirm the option by ps:

$ ps xafu | grep slapd
ldap     10109  0.0  0.0 543936 10444 ?        Ssl  10:50   0:00 /usr/sbin/slapd -u ldap -h ldapi:/// ldap:/// ldaps:/// -s 256

however, I cannot confirm any logs by the following command.

$ sudo journalctl --follow _SYSTEMD_UNIT=slapd.service

While I change olcLogLevel to other than 0 (e.g. 256) by:

$ sudo ldapmodify -Y EXTERNAL -H ldapi:/// <<EOF
dn:           cn=config
changetype:   modify
replace:      olcLogLevel
olcLogLevel:  256
EOF

(I can confirm if it is set by the following command)

$ sudo grep olcLogLevel /etc/openldap/slapd.d/cn=config.ldif
olcLogLevel: 256

then do ldapsearch:

$ ldapsearch -x -H ldap://localhost -b dc=csc -s base
...

so we see loglevel=256 logs by:

$ sudo journalctl --follow _SYSTEMD_UNIT=slapd.service
Dec 12 10:59:40 my-host slapd[10537]: conn=1003 fd=13 ACCEPT from IP=[::1]:41078 (IP=[::]:389)
Dec 12 10:59:40 my-host slapd[10537]: conn=1003 fd=13 closed
...

This means:

• -d overwrite olcLogLevel
• -s doesn't overwrite olcLogLevel

Is my understanding right? If yes, what is the '-s' option?

My OS version is:

$ cat /etc/centos-release
CentOS Linux release 7.9.2009 (Core)

slpad version is:

$ sudo yum list installed | grep openldap
openldap.x86_64                             2.4.44-23.el7_9            @updates