tail--命令详解
tail：显示文件内容尾部
功能说明：用于显示文件内容的尾部，默认输出文件的最后10行。
语法格式： tail 【option】 【file】
tail 选项 文件
参数： -n 指定显示的行数
[root@template ~ 15:08:16]]# tail /etc/passwd #不加-n默认输出末尾10行
abrt:x:173:173::/etc/abrt:/sbin/nologin
sshd:x:74:74:Privilege-separated SSH:/var/empty/sshd:/sbin/nologin
postfix:x:89:89::/var/spool/postfix:/sbin/nologin
rpc:x:32:32:Rpcbind Daemon:/var/lib/rpcbind:/sbin/nologin
rpcuser:x:29:29:RPC Service User:/var/lib/nfs:/sbin/nologin
nfsnobody:x:65534:65534:Anonymous NFS User:/var/lib/nfs:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin
nginx:x:111:1000::/home/nginx:/sbin/nologin
openvpn:x:998:996:OpenVPN:/etc/openvpn:/sbin/nologin
redis:x:2000:2000::/home/redis:/sbin/nologin
[root@template ~ 15:08:52]]# tail -n 5 /etc/passwd #第二种写法可以写成 tail -5 /etc/passwd
nfsnobody:x:65534:65534:Anonymous NFS User:/var/lib/nfs:/sbin/nologin
ntp:x:38:38::/etc/ntp:/sbin/nologin
nginx:x:111:1000::/home/nginx:/sbin/nologin
openvpn:x:998:996:OpenVPN:/etc/openvpn:/sbin/nologin
redis:x:2000:2000::/home/redis:/sbin/nologin
参数：-f 实时输出文件变化后追加的数据
[root@template ~ 15:11:57]]# tail -f /opt/redis_6380/logs/redis_6380.log #实时监控redis的日志文件的变化
1821:M 28 Feb 2021 23:22:42.466 * FAIL message received from dfeaed753633b76bc38f2dcc28143e18db256357 about 7f0af1b25784d2d8a8eed8cce54df1e5b8720590
1821:M 28 Feb 2021 23:22:42.466 * FAIL message received from dfeaed753633b76bc38f2dcc28143e18db256357 about 420b366762033aa92bdce76ccf30a7bb0acc6e33
1821:M 28 Feb 2021 23:22:42.873 # Failover auth granted to 13c20233f64261bac6d1f412418de98eb8d91f5e for epoch 12
1821:M 28 Feb 2021 23:23:43.775 # Failover auth granted to 13c20233f64261bac6d1f412418de98eb8d91f5e for epoch 13
1821:M 28 Feb 2021 23:24:44.769 # Failover auth granted to 13c20233f64261bac6d1f412418de98eb8d91f5e for epoch 14
1821:M 01 Mar 2021 00:22:27.609 * Replication backlog freed after 3600 seconds without connected replicas.
1821:M 01 Mar 2021 08:39:17.048 # User requested shutdown...
1821:M 01 Mar 2021 08:39:17.048 * Calling fsync() on the AOF file.
1821:M 01 Mar 2021 08:39:17.048 * Removing the pid file.
1821:M 01 Mar 2021 08:39:17.048 # Redis is now ready to exit, bye bye...
参数：-F 实时输出文件变化后追加的数据，不会因为文件不存在了就自动退出
[root@template ~ 15:14:37]]# tail -F /opt/redis_6380/logs/redis_6380.log #当文件不存在时会返回报错，不会退出一直等待文件生成。
1821:M 28 Feb 2021 23:22:42.466 * FAIL message received from dfeaed753633b76bc38f2dcc28143e18db256357 about 7f0af1b25784d2d8a8eed8cce54df1e5b8720590
1821:M 28 Feb 2021 23:22:42.466 * FAIL message received from dfeaed753633b76bc38f2dcc28143e18db256357 about 420b366762033aa92bdce76ccf30a7bb0acc6e33
1821:M 28 Feb 2021 23:22:42.873 # Failover auth granted to 13c20233f64261bac6d1f412418de98eb8d91f5e for epoch 12
1821:M 28 Feb 2021 23:23:43.775 # Failover auth granted to 13c20233f64261bac6d1f412418de98eb8d91f5e for epoch 13
1821:M 28 Feb 2021 23:24:44.769 # Failover auth granted to 13c20233f64261bac6d1f412418de98eb8d91f5e for epoch 14
1821:M 01 Mar 2021 00:22:27.609 * Replication backlog freed after 3600 seconds without connected replicas.
1821:M 01 Mar 2021 08:39:17.048 # User requested shutdown...
补充备注：tailf==tail -f
