ubuntu@ip-172-31-32-10:/etc/kamailio$ kamctl ul show
ERROR: Error opening Kamailio's FIFO /var/run/kamailio/kamailio_fifo
ERROR: Make sure you have the line 'modparam("mi_fifo", "fifo_name", "/var/run/kamailio/kamailio_fifo")' in your config
ERROR: and also have loaded the mi_fifo module.

#my FIFO file

ubuntu@ip-172-31-32-10:/etc/kamailio$ ls -l /var/run/kamailio/kamailio_fifo
prw-rw---- 1 kamailio kamailio 0 Oct  7 09:01 /var/run/kamailio/kamailio_fifo

#FIFO in config

ubuntu@ip-172-31-32-10:/etc/kamailio$ grep fifo kamailio.cfg
loadmodule "mi_fifo.so"
# ----- mi_fifo params -----
modparam("mi_fifo", "fifo_name", "/var/run/kamailio/kamailio_fifo")

#With sudo it works

ubuntu@ip-172-31-32-10:/etc/kamailio$ sudo kamctl ul show
Domain:: location table=1024 records=0 max_slot=0

Further ...

ubuntu@ip-172-31-32-10:/etc/kamailio$ kamctl restart

INFO: Stopping Kamailio :

ERROR: No PID file found (/var/run/kamailio.pid)! Kamailio probably not running
INFO: check with 'ps axw | /bin/egrep kamailio'

#But kamailio is running

ubuntu@ip-172-31-32-10:/etc/kamailio$ ps axw|egrep kamailio
 4122 ?        S      0:00 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4123 ?        S      0:00 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4124 ?        S      0:00 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4125 ?        S      0:00 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4126 ?        S      0:00 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4127 ?        S      0:46 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4128 ?        S      0:44 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4129 ?        S      0:44 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4130 ?        S      0:44 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4131 ?        S      0:03 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4132 ?        S    909:27 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4133 ?        S      0:00 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4134 ?        S      5:08 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4135 ?        S     25:51 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4136 ?        S     26:02 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4137 ?        S     26:08 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4138 ?        S     26:18 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
 4139 ?        S     10:17 /usr/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 64 -M 8 -u kamailio -g kamailio
27344 pts/1    S+     0:00 egrep --color=auto kamailio

Whats wrong with my usage of kamctl?

Thanks Hermann