[Serusers] why i cannot use "serctl moni"?

[C Y]

Hi,everyone
why i cannot use "serctl moni"?I have run the command :export 
SIP_DOMAIN="voipv6.edu.cn".
And the error is :
# serctl  moni
Error opening ser's FIFO /tmp/ser_fifo
Make sure you have line fifo=/tmp/ser_fifo in your config

And I did have the line :

check_via=yes   # (cmd. line: -v)
dns=yes           # (cmd. line: -r)
rev_dns=yes      # (cmd. line: -R)
port=5060
#children=4
fifo="/tmp/ser_fifo"

what should i do to solve the problem?

These are some informations  related to my setting and problem:
     1、operating system:Linux 7.0
     2、SER distribution: ser-0.8.14_linux_i386.tar.gz

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