Re: pg_dumpall: could not connect to database "template1": FATAL:

For example: How can I restart the SQL server? Oh sorry we can't help
you with this … ?

https://www.postgresql.org/docs/9.5/static/app-pg-ctl.html

the best way of doing this depends on the way postgres was installed, and varies by OS/distribution.    for instance, on RHEL/CentOS <= 6,

    service postgresql-X.Y restart

on RHEL/CentOS 7

    systemctl restart postgresql-X.Y

(both these run by root, or via sudo)

-- 
john r pierce, recycling bits in santa cruz