1、检查数据库版本：

postgres=# select version();
                                                   version                      
                             
--------------------------------------------------------------------------------
-----------------------------
 Postgresql 9.4.2 on x86_64-redhat-linux-gnu,compiled by gcc (GCC) 5.1.1 201504
22 (Red Hat 5.1.1-1),64-bit
(1 行记录)

2、查看数据库启动时间：

postgres=# select pg_postmaster_start_time();
   pg_postmaster_start_time    
-------------------------------
 2015-06-12 19:06:23.031591+08

截至当前时间，运行了多长时间：

postgres=# select current_timestamp - pg_postmaster_start_time() as uptime;
     uptime      
-----------------
 02:34:13.631323

postgres=# select date_trunc('second',current_timestamp-pg_postmaster_start_time()) as uptime;
  uptime  
----------
 02:36:10

3、列出当前所有数据库：

bash-4.3$ psql -l
                                     资料库列表
   名称    |  拥有者  | 字元编码 |  校对规则   |    Ctype    |       存取权限        
-----------+----------+----------+-------------+-------------+-----------------------
 postgres  | postgres | UTF8     | zh_CN.UTF-8 | zh_CN.UTF-8 | 
 template0 | postgres | UTF8     | zh_CN.UTF-8 | zh_CN.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
 template1 | postgres | UTF8     | zh_CN.UTF-8 | zh_CN.UTF-8 | =c/postgres          +
           |          |          |             |             | postgres=CTc/postgres
(3 行记录)

或

ostgres=# select datname from pg_database;
  datname  
-----------
 template1
 template0
 postgres
(3 行记录)

4、查看数据库文件大小

postgres=# select pg_database_size(current_database());
 pg_database_size 
------------------
          6999828

上面是当前数据库

postgres=# select current_database();
 current_database 
------------------
 postgres

或者所有数据库文件大小：

postgres=# select sum(pg_database_size(datname)) from pg_database;
   sum    
----------
 20738844
(1 行记录)