忘记postgres用户密码怎么办？

环境：
Ubuntu 16.04
postgres : apt-get install postgresql 9.5版本

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sudo vim /etc/postgresql/9.5/main/pg_hba.conf
修改下面ipv4登录md5为trust.

local   all             postgres                                peer

# TYPE  DATABASE        USER            ADDRESS                 METHOD

# "local" is for Unix domain socket connections only
local   all             all                                     peer
# IPv4 local connections:
host    all             all             127.0.0.1/32            md5
# IPv6 local connections:
host    all             all             ::1/128                 md5

重启postgressql服务。
~$ systemctl restart postgresq
免密码登录

parallels@parallels-vm:~$ psql -U postgres -h 127.0.0.1
psql (9.5.12)
SSL connection (protocol: TLSv1.2, cipher: ECDHE-RSA-AES256-GCM-SHA384, bits: 256, compression: off)
Type "help" for help.
postgres=#

修改密码并退出

postgres=# alter user postgres with password '123';
ALTER ROLE
postgres=# \q

修改回认证并退出： trust改为md5
sudo vim /etc/postgresql/9.5/main/pg_hba.conf

# IPv4 local connections:
host    all             all             127.0.0.1/32            trust

重启并登陆：

parallels@parallels-vm:~$ systemctl restart postgresql
parallels@parallels-vm:~$ psql -U postgres -h 127.0.0.1
Password for user postgres: 
psql (9.5.12)
SSL connection (protocol: TLSv1.2, cipher: ECDHE-RSA-AES256-GCM-SHA384, bits: 256, compression: off)
Type "help" for help.

(完)