Can't open PID file /run/opendkim/opendkim.pid (yet?) after start: Operation not permitted

i am about 2 hours on configure dkim with postfix on ubuntu 20.04. I try absolutly everything, but dkim wont work.

OpenDKIM-Service won´t start:

root@mail:~# service opendkim status
● opendkim.service - OpenDKIM DomainKeys Identified Mail (DKIM) Milter
     Loaded: loaded (/lib/systemd/system/opendkim.service; enabled; vendor preset: enabled)
     Active: activating (start) since Sat 2022-01-08 19:39:15 CET; 59s ago
       Docs: man:opendkim(8)
             man:opendkim.conf(5)
             man:opendkim-genkey(8)
             man:opendkim-genzone(8)
             man:opendkim-testadsp(8)
             man:opendkim-testkey
             http://www.opendkim.org/docs.html
    Process: 62335 ExecStart=/usr/sbin/opendkim -x /etc/opendkim.conf (code=exited, status=0/SUCCESS)
      Tasks: 7 (limit: 19660)
     Memory: 2.7M
     CGroup: /system.slice/opendkim.service
             ├─62336 /usr/sbin/opendkim -x /etc/opendkim.conf
             └─62337 /usr/sbin/opendkim -x /etc/opendkim.conf

Jan 08 19:39:15 mail.mydomain.de systemd[1]: Starting OpenDKIM DomainKeys Identified Mail (DKIM) Milter...
Jan 08 19:39:15 mail.mydomain.de systemd[1]: opendkim.service: Can't open PID file /run/opendkim/opendkim.pid (yet?) after start: Operation not permitted
Jan 08 19:39:15 mail.mydomain.de opendkim[62337]: OpenDKIM Filter v2.11.0 starting (args: -x /etc/opendkim.conf)
Jan 07 13:32:59 mail.mydomain.de systemd[1]: Starting OpenDKIM DomainKeys Identified Mail (DKIM) Milter...
Jan 07 13:32:59 mail.mydomain.de systemd[1]: Started OpenDKIM DomainKeys Identified Mail (DKIM) Milter.
Jan 07 13:32:59 mail.mydomain.de opendkim[275965]: OpenDKIM Filter v2.11.0 starting (args: -x /etc/opendkim.conf)
Jan 08 10:35:44 mail.mydomain.de systemd[1]: Stopping OpenDKIM DomainKeys Identified Mail (DKIM) Milter...
Jan 08 10:35:50 mail.mydomain.de systemd[1]: opendkim.service: Succeeded.
Jan 08 10:35:50 mail.mydomain.de systemd[1]: Stopped OpenDKIM DomainKeys Identified Mail (DKIM) Milter.

Here is my /etc/opendkim.conf:

# This is a basic configuration that can easily be adapted to suit a standard
# installation. For more advanced options, see opendkim.conf(5) and/or
# /usr/share/doc/opendkim/examples/opendkim.conf.sample.

# Log to syslog
Syslog          yes
# Required to use local socket with MTAs that access the socket as a non-
# privileged user (e.g. Postfix)
UMask           002

# Sign for example.com with key in /etc/dkimkeys/dkim.key using
# selector '2007' (e.g. 2007._domainkey.example.com)
#Domain         example.com
#KeyFile        /etc/dkimkeys/dkim.key
#Selector       2007

# Commonly-used options; the commented-out versions show the defaults.
Canonicalization    simple
Mode            sv
SubDomains      no
AutoRestart         yes
AutoRestartRate     10/1M
Background          yes
DNSTimeout          5
SignatureAlgorithm  rsa-sha256

# Always oversign From (sign using actual From and a null From to prevent
# malicious signatures header fields (From and/or others) between the signer
# and the verifier.  From is oversigned by default in the Debian pacakge
# because it is often the identity key used by reputation systems and thus
# somewhat security sensitive.
OversignHeaders     From

##  ResolverConfiguration filename
##      default (none)
##
##  Specifies a configuration file to be passed to the Unbound library that
##  performs DNS queries applying the DNSSEC protocol.  See the Unbound
##  documentation at http://unbound.net for the expected content of this file.
##  The results of using this and the TrustAnchorFile setting at the same
##  time are undefined.
##  In Debian, /etc/unbound/unbound.conf is shipped as part of the Suggested
##  unbound package

# ResolverConfiguration     /etc/unbound/unbound.conf

##  TrustAnchorFile filename
##      default (none)
##
## Specifies a file from which trust anchor data should be read when doing
## DNS queries and applying the DNSSEC protocol.  See the Unbound documentation
## at http://unbound.net for the expected format of this file.

TrustAnchorFile       /usr/share/dns/root.key

#OpenDKIM user
# Remember to add user postfix to group opendkim
UserID             opendkim

# Map domains in From addresses to keys used to sign messages
KeyTable           refile:/etc/opendkim/key.table
SigningTable       refile:/etc/opendkim/signing.table

# Hosts to ignore when verifying signatures
ExternalIgnoreList  /etc/opendkim/trusted.hosts

# A set of internal hosts whose mail should be signed
InternalHosts       /etc/opendkim/trusted.hosts

Socket    local:/var/spool/postfix/opendkim/opendkim.sock

Here is my /etc/default/opendkim.conf

# Command-line options specified here will override the contents of
# /etc/opendkim.conf. See opendkim(8) for a complete list of options.
#DAEMON_OPTS=""
#
# Uncomment to specify an alternate socket
# Note that setting this will override any Socket value in opendkim.conf
# default:
SOCKET="local:/var/spool/postfix/opendkim/opendkim.sock"
# listen on all interfaces on port 54321:
#SOCKET="inet:54321"
# listen on loopback on port 12345:
#SOCKET="inet:12345@localhost"
# listen on 192.0.2.1 on port 12345:
#SOCKET="inet:12345@192.0.2.1"

Here is my master.cf:

#
# Postfix master process configuration file.  For details on the format
# of the file, see the master(5) manual page (command: "man 5 master" or
# on-line: http://www.postfix.org/master.5.html).
#
# Do not forget to execute "postfix reload" after editing this file.
#
# ==========================================================================
# service type  private unpriv  chroot  wakeup  maxproc command + args
#               (yes)   (yes)   (no)    (never) (100)
# ==========================================================================
smtp       inet  n       -       y       -       -       smtpd
#smtp      inet  n       -       y       -       1       postscreen
#smtpd     pass  -       -       y       -       -       smtpd
#dnsblog   unix  -       -       y       -       0       dnsblog
#tlsproxy  unix  -       -       y       -       0       tlsproxy
submission inet  n       -       y       -       -       smtpd
  -o smtpd_enforce_tls=yes
  -o smtpd_sasl_auth_enable=yes
  -o smtpd_client_restrictions=permit_sasl_authenticated,reject
#  -o syslog_name=postfix/submission
#  -o smtpd_tls_security_level=encrypt
#  -o smtpd_sasl_auth_enable=yes
#  -o smtpd_tls_auth_only=yes
#  -o smtpd_reject_unlisted_recipient=no
#  -o smtpd_client_restrictions=$mua_client_restrictions
#  -o smtpd_helo_restrictions=$mua_helo_restrictions
#  -o smtpd_sender_restrictions=$mua_sender_restrictions
#  -o smtpd_recipient_restrictions=
#  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
#  -o milter_macro_daemon_name=ORIGINATING
#smtps     inet  n       -       y       -       -       smtpd
#  -o syslog_name=postfix/smtps
#  -o smtpd_tls_wrappermode=yes
#  -o smtpd_sasl_auth_enable=yes
#  -o smtpd_reject_unlisted_recipient=no
#  -o smtpd_client_restrictions=$mua_client_restrictions
#  -o smtpd_helo_restrictions=$mua_helo_restrictions
#  -o smtpd_sender_restrictions=$mua_sender_restrictions
#  -o smtpd_recipient_restrictions=
#  -o smtpd_relay_restrictions=permit_sasl_authenticated,reject
#  -o milter_macro_daemon_name=ORIGINATING
#628       inet  n       -       y       -       -       qmqpd
pickup    unix  n       -       y       60      1       pickup
cleanup   unix  n       -       y       -       0       cleanup
qmgr      unix  n       -       n       300     1       qmgr
#qmgr     unix  n       -       n       300     1       oqmgr
tlsmgr    unix  -       -       y       1000?   1       tlsmgr
rewrite   unix  -       -       y       -       -       trivial-rewrite
bounce    unix  -       -       y       -       0       bounce
defer     unix  -       -       y       -       0       bounce
trace     unix  -       -       y       -       0       bounce
verify    unix  -       -       y       -       1       verify
flush     unix  n       -       y       1000?   0       flush
proxymap  unix  -       -       n       -       -       proxymap
proxywrite unix -       -       n       -       1       proxymap
smtp      unix  -       -       y       -       -       smtp
relay     unix  -       -       y       -       -       smtp
        -o syslog_name=postfix/$service_name
#       -o smtp_helo_timeout=5 -o smtp_connect_timeout=5
showq     unix  n       -       y       -       -       showq
error     unix  -       -       y       -       -       error
retry     unix  -       -       y       -       -       error
discard   unix  -       -       y       -       -       discard
local     unix  -       n       n       -       -       local
virtual   unix  -       n       n       -       -       virtual
lmtp      unix  -       -       y       -       -       lmtp
anvil     unix  -       -       y       -       1       anvil
scache    unix  -       -       y       -       1       scache
postlog   unix-dgram n  -       n       -       1       postlogd
#
# ====================================================================
# Interfaces to non-Postfix software. Be sure to examine the manual
# pages of the non-Postfix software to find out what options it wants.
#
# Many of the following services use the Postfix pipe(8) delivery
# agent.  See the pipe(8) man page for information about ${recipient}
# and other message envelope options.
# ====================================================================
#
# maildrop. See the Postfix MAILDROP_README file for details.
# Also specify in main.cf: maildrop_destination_recipient_limit=1
#
maildrop  unix  -       n       n       -       -       pipe
  flags=DRhu user=vmail argv=/usr/bin/maildrop -d ${recipient}
#
# ====================================================================
#
# Recent Cyrus versions can use the existing "lmtp" master.cf entry.
#
# Specify in cyrus.conf:
#   lmtp    cmd="lmtpd -a" listen="localhost:lmtp" proto=tcp4
#
# Specify in main.cf one or more of the following:
#  mailbox_transport = lmtp:inet:localhost
#  virtual_transport = lmtp:inet:localhost
#
# ====================================================================
#
# Cyrus 2.1.5 (Amos Gouaux)
# Also specify in main.cf: cyrus_destination_recipient_limit=1
#
#cyrus     unix  -       n       n       -       -       pipe
#  user=cyrus argv=/cyrus/bin/deliver -e -r ${sender} -m ${extension} ${user}
#
# ====================================================================
# Old example of delivery via Cyrus.
#
#old-cyrus unix  -       n       n       -       -       pipe
#  flags=R user=cyrus argv=/cyrus/bin/deliver -e -m ${extension} ${user}
#
# ====================================================================
#
# See the Postfix UUCP_README file for configuration details.
#
uucp      unix  -       n       n       -       -       pipe
  flags=Fqhu user=uucp argv=uux -r -n -z -a$sender - $nexthop!rmail ($recipient)
#
# Other external delivery methods.
#
ifmail    unix  -       n       n       -       -       pipe
  flags=F user=ftn argv=/usr/lib/ifmail/ifmail -r $nexthop ($recipient)
bsmtp     unix  -       n       n       -       -       pipe
  flags=Fq. user=bsmtp argv=/usr/lib/bsmtp/bsmtp -t$nexthop -f$sender $recipient
scalemail-backend unix  -   n   n   -   2   pipe
  flags=R user=scalemail argv=/usr/lib/scalemail/bin/scalemail-store ${nexthop} ${user} ${extension}
mailman   unix  -       n       n       -       -       pipe
  flags=FR user=list argv=/usr/lib/mailman/bin/postfix-to-mailman.py
  ${nexthop} ${user}

smtps      inet  n       -       y       -       -       smtpd
    -o smtpd_tls_wrappermode=yes  

Here is my /etc/postfix/main.cf:

# See /usr/share/postfix/main.cf.dist for a commented, more complete version


# Debian specific:  Specifying a file name will cause the first
# line of that file to be used as the name.  The Debian default
# is /etc/mailname.
#myorigin = /etc/mailname

smtpd_banner = $myhostname ESMTP 
myhostname = mail.mydomain.de
biff = no

# appending .domain is the MUA's job.
append_dot_mydomain = no

# Uncomment the next line to generate "delayed mail" warnings
#delay_warning_time = 4h

readme_directory = no

# See http://www.postfix.org/COMPATIBILITY_README.html -- default to 2 on
# fresh installs.
compatibility_level = 2
message_size_limit = 10240000

# TLS parameters
smtpd_tls_cert_file=/etc/ssl/certs/ssl-cert-snakeoil.pem
smtpd_tls_key_file=/etc/ssl/private/ssl-cert-snakeoil.key
smtpd_tls_security_level=may

smtp_tls_CApath=/etc/ssl/certs
smtp_tls_security_level=may
smtp_tls_session_cache_database = btree:${data_directory}/smtp_scache

smtpd_recipient_restrictions = permit_mynetworks, reject_unauth_destination, reject_non_fqdn_sender
# Milter configuration
milter_default_action = accept
milter_protocol = 6
smtpd_milters = local:opendkim/opendkim.sock
non_smtpd_milters = $smtpd_milters
smtpd_sender_restrictions = permit_mynetworks, permit_sasl_authenticated
mynetworks = 127.0.0.0/8 [::ffff:127.0.0.0]/104 [::1]/128

alias_maps = hash:/etc/aliases
alias_database = hash:/etc/aliases
myorigin = /etc/mailname
mydestination = localhost
relayhost =
smtpd_relay_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_unauth_destination
mailbox_command = procmail -a "$EXTENSION"
mailbox_size_limit = 0
recipient_delimiter = +
inet_interfaces = all
inet_protocols = all

#custom for kopano
virtual_alias_maps = hash:/etc/postfix/virtual
virtual_mailbox_maps = mysql:/etc/postfix/mysql-users.cf
virtual_transport = lmtp:[localhost]:2003
virtual_mailbox_domains = mydomain1.de, mydomain2.de
#

smtpd_tls_ciphers = medium
smtpd_tls_mandatory_ciphers = medium
tls_medium_cipherlist = ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384
smtpd_tls_mandatory_protocols = TLSv1.2
smtpd_tls_protocols = TLSv1.2
smtpd_tls_security_level = may
smtp_tls_security_level = may
smtp_use_tls = no


smtpd_client_restrictions = permit_mynetworks, permit_sasl_authenticated, reject_rbl_client zen.spamhaus.org
smtp_send_xforward_command = yes
smtpd_authorized_xforward_hosts = 127.0.0.0/8 [::1]/128
smtpd_sasl_auth_enable = no
virtual_mailbox_base = /var/qmail/mailnames
virtual_uid_maps = static:30
virtual_gid_maps = static:31

I'm seeing the same problem. I don't have enough reputation to leave a comment so leaving an observation not really an answer which might help lead to a better answer. Hopefully.

creating the file helped get opendkim to startup. touch /run/opendkim/opendkim.pid

Then I found you have to change the ownership on the file in which I just did the entire folder. chown -R opendkim /run/opedkim

I believe the problem starts there in that the file then changes ownership back to root and the next time the process is started I get the same error.

systemd[1]: opendkim.service: Can't open PID file /run/opendkim.pid (yet?) after start: Operation not permitted

So mostly looks like an ownership problem and prior to that a file doesn't exist problem.

I'm still investigating and I still seem to have an issue that the socket local:/var/spool/postfix/opendkim/opendkim.sock isn't being created and then postfix is complaining even though opendkim is running. So it's a two layered problem I'm dealing with, but thought I would add my observation.

Oh, and I'm using Debian

After more investigation and reading the comment(s) above I'm also convinced that this is a non-error that can be ignored.

You are running your postfix in a chroot:

SOCKET="local:/var/spool/postfix/opendkim/opendkim.sock"

But systemd is trying to check

/run/opendkim/opendkim.pid