1.查看内存和释放内存：
查看内存：free -m
释放内存：echo 1 > /proc/sys/vm/drop_caches
2.查看用户和用户组：
cat /etc/passwd
结果如下：
root:x:0:0:root:/root:/bin/bashbin:x:1:1:bin:/bin:/sbin/nologindaemon:x:2:2:daemon:/sbin:/sbin/nologinadm:x:3:4:adm:/var/adm:/sbin/nologinlp:x:4:7:lp:/var/spool/lpd:/sbin/nologinsync:x:5:0:sync:/sbin:/bin/syncshutdown:x:6:0:shutdown:/sbin:/sbin/shutdownhalt:x:7:0:halt:/sbin:/sbin/haltmail:x:8:12:mail:/var/spool/mail:/sbin/nologinuucp:x:10:14:uucp:/var/spool/uucp:/sbin/nologinoperator:x:11:0:operator:/root:/sbin/nologingames:x:12:100:games:/usr/games:/sbin/nologingopher:x:13:30:gopher:/var/gopher:/sbin/nologinftp:x:14:50:FTP User:/var/ftp:/sbin/nologinnobody:x:99:99:Nobody:/:/sbin/nologindbus:x:81:81:System message bus:/:/sbin/nologinrpc:x:32:32:Rpcbind Daemon:/var/lib/rpcbind:/sbin/nologinvcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologinabrt:x:173:173::/etc/abrt:/sbin/nologinrpcuser:x:29:29:RPC Service User:/var/lib/nfs:/sbin/nologinnfsnobody:x:65534:65534:Anonymous NFS User:/var/lib/nfs:/sbin/nologinhaldaemon:x:68:68:HAL daemon:/:/sbin/nologinntp:x:38:38::/etc/ntp:/sbin/nologinsaslauth:x:499:76:Saslauthd user:/var/empty/saslauth:/sbin/nologinpostfix:x:89:89::/var/spool/postfix:/sbin/nologinsshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologinoprofile:x:16:16:Special user account to be used by OProfile:/home/oprofile:/sbin/nologintcpdump:x:72:72::/:/sbin/nologinmysql:x:27:27:MySQL Server:/var/lib/mysql:/bin/bashapache:x:48:48:Apache:/var/www:/sbin/nologinzookeeper:x:498:498:ZooKeeper:/var/lib/zookeeper:/sbin/nologinmailnull:x:47:47::/var/spool/mqueue:/sbin/nologinsmmsp:x:51:51::/var/spool/mqueue:/sbin/nologinsolr:x:497:497:Solr:/var/lib/solr:/sbin/nologinhbase:x:496:496:HBase:/var/lib/hbase:/sbin/nologinhive:x:495:495:Hive:/var/lib/hive:/sbin/nologinsentry:x:494:494:Sentry:/var/lib/sentry:/sbin/nologinhdfs:x:493:492:Hadoop HDFS:/var/lib/hadoop-hdfs:/bin/bashyarn:x:492:491:Hadoop Yarn:/var/lib/hadoop-yarn:/bin/bashimpala:x:491:490:Impala:/var/lib/impala:/bin/bashmapred:x:490:489:Hadoop MapReduce:/var/lib/hadoop-mapreduce:/bin/bashhue:x:500:500::/home/hue:/bin/bash
3. vim 撤销、回退操作：
u：撤销上一步的操作；
Ctrl+r：恢复上一步被撤销的操作。
4.
转载于:https://www.cnblogs.com/mediocreWorld/p/11070632.html
