I'm probably overlooking a typo, but i cant find it.
~$ /usr/bin/ldapmodify -H ldapi:// -Y EXTERNAL -f /tmp/certs.ldif
SASL/EXTERNAL authentication started
SASL username:
gidNumber=0+uidNumber=0,cn=peercred,cn=external,cn=auth
SASL SSF: 0
modifying entry "cn=config"
ldap_modify: Other (e.g., implementation specific) error (80)
~$ cat /tmp/certs.ldif
dn: cn=config
changetype: modify
replace: olcTLSCertificateFile
olcTLSCertificateFile: /etc/openldap/certs/ldap.crt
grep -R olcTLS /etc/openldap/slapd.d
/etc/openldap/slapd.d/cn=config.ldif:olcTLSCACertificatePa th: /etc/openldap/certs
/etc/openldap/slapd.d/cn=config.ldif:olcTLSCertificateFile: "OpenLDAP Server"
/etc/openldap/slapd.d/cn=config.ldif:olcTLSCertificateKeyFile: /etc/openldap/certs/password
ls -la /etc/openldap/certs/ldap.crt
-rw-r--r--. 1 root root 2282 Aug 20 17:42 /etc/openldap/certs/ldap.crt