命令讲解：
tail命令
tail {文件} 显示指定 文件末尾 内容（默认显示10行）
tail -f {文件} -f 动态 刷新 循环读取 显示文件里的最尾部的内容显示在屏幕上，并且不断刷新，只要 filename 更新就可以看到最新的文件内容。
tail -c {字节数} {文件} -c 按字节数 显示 文件末尾 内容
tail -n {行数} {文件} -n 按行数 显示 文件末尾 内容
实操验证：
[154.8.159.209:root@xlp117 /var/www/html/log]# tail -f node-access.log
2020-03-19 14:39:54 +08:00: <-- POST /pdd/sms/status?appid=1400155389
2020-03-19 14:39:54 +08:00: --> POST /pdd/sms/status?appid=1400155389 200 2ms 26b
2020-03-19 14:42:52 +08:00: <-- GET /pdd/sms/sendMulti?action=send&verifymethod=pwd&loginid=100000&loginpwd=c0eb9f2d0b353dc9a2e5d5b2c97dc80b&mobiles=13681314935&channel=&uid=&extend=102556301&content=0%10e%B0%80T%90%1AO%E10%11%60%A8v%84%9A%8C%8B%C1x%01f%2F%002&msgfmt=8&uuid=1494363028144520720&original_cloud=&sender=cmmp_sv_100017
2020-03-19 14:42:52 +08:00: 3333
2020-03-19 14:42:52 +08:00: --> GET /pdd/sms/sendMulti?action=send&verifymethod=pwd&loginid=100000&loginpwd=c0eb9f2d0b353dc9a2e5d5b2c97dc80b&mobiles=13681314935&channel=&uid=&extend=102556301&content=0%10e%B0%80T%90%1AO%E10%11%60%A8v%84%9A%8C%8B%C1x%01f%2F%002&msgfmt=8&uuid=1494363028144520720&original_cloud=&sender=cmmp_sv_100017 200 55ms 58b
2020-03-19 17:16:42 +08:00: <-- GET /pdd/sms/sendMulti?action=send&verifymethod=pwd&loginid=100000&loginpwd=c0eb9f2d0b353dc9a2e5d5b2c97dc80b&mobiles=13681314935&channel=&uid=&extend=102556301&content=0%10e%B0%80T%90%1AO%E10%11%60%A8v%84%9A%8C%8B%C1x%01f%2F%002&msgfmt=8&uuid=1494363028144520720&original_cloud=&sender=cmmp_sv_100017
2020-03-19 17:16:42 +08:00: --> GET /pdd/sms/sendMulti?action=send&verifymethod=pwd&loginid=100000&loginpwd=c0eb9f2d0b353dc9a2e5d5b2c97dc80b&mobiles=13681314935&channel=&uid=&extend=102556301&content=0%10e%B0%80T%90%1AO%E10%11%60%A8v%84%9A%8C%8B%C1x%01f%2F%002&msgfmt=8&uuid=1494363028144520720&original_cloud=&sender=cmmp_sv_100017 200 37ms 58b
2020-03-19 17:22:43 +08:00: <-- GET /pdd/sms/sendMulti?action=send&verifymethod=pwd&loginid=100000&loginpwd=c0eb9f2d0b353dc9a2e5d5b2c97dc80b&mobiles=13681314935&channel=&uid=&extend=102556301&content=0%10e%B0%80T%90%1AO%E10%11%60%A8v%84%9A%8C%8B%C1x%01f%2F%002&msgfmt=8&uuid=1494363028144520720&original_cloud=&sender=cmmp_sv_100017
2020-03-19 17:22:43 +08:00: --> GET /pdd/sms/sendMulti?action=send&verifymethod=pwd&loginid=100000&loginpwd=c0eb9f2d0b353dc9a2e5d5b2c97dc80b&mobiles=13681314935&channel=&uid=&extend=102556301&content=0%10e%B0%80T%90%1AO%E10%11%60%A8v%84%9A%8C%8B%C1x%01f%2F%002&msgfmt=8&uuid=1494363028144520720&original_cloud=&sender=cmmp_sv_100017 200 35ms 58b
2020-03-19 17:22:43 +08:00: 1
[154.8.159.209:root@xlp117 /var/www/html/log]# tail -c 5 node-access.log
0: 1
[154.8.159.209:root@xlp117 /var/www/html/log]# tail -n 5 node-access.log
2020-03-19 17:16:42 +08:00: <-- GET /pdd/sms/sendMulti?action=send&verifymethod=pwd&loginid=100000&loginpwd=c0eb9f2d0b353dc9a2e5d5b2c97dc80b&mobiles=13681314935&channel=&uid=&extend=102556301&content=0%10e%B0%80T%90%1AO%E10%11%60%A8v%84%9A%8C%8B%C1x%01f%2F%002&msgfmt=8&uuid=1494363028144520720&original_cloud=&sender=cmmp_sv_100017
2020-03-19 17:16:42 +08:00: --> GET /pdd/sms/sendMulti?action=send&verifymethod=pwd&loginid=100000&loginpwd=c0eb9f2d0b353dc9a2e5d5b2c97dc80b&mobiles=13681314935&channel=&uid=&extend=102556301&content=0%10e%B0%80T%90%1AO%E10%11%60%A8v%84%9A%8C%8B%C1x%01f%2F%002&msgfmt=8&uuid=1494363028144520720&original_cloud=&sender=cmmp_sv_100017 200 37ms 58b
2020-03-19 17:22:43 +08:00: <-- GET /pdd/sms/sendMulti?action=send&verifymethod=pwd&loginid=100000&loginpwd=c0eb9f2d0b353dc9a2e5d5b2c97dc80b&mobiles=13681314935&channel=&uid=&extend=102556301&content=0%10e%B0%80T%90%1AO%E10%11%60%A8v%84%9A%8C%8B%C1x%01f%2F%002&msgfmt=8&uuid=1494363028144520720&original_cloud=&sender=cmmp_sv_100017
2020-03-19 17:22:43 +08:00: --> GET /pdd/sms/sendMulti?action=send&verifymethod=pwd&loginid=100000&loginpwd=c0eb9f2d0b353dc9a2e5d5b2c97dc80b&mobiles=13681314935&channel=&uid=&extend=102556301&content=0%10e%B0%80T%90%1AO%E10%11%60%A8v%84%9A%8C%8B%C1x%01f%2F%002&msgfmt=8&uuid=1494363028144520720&original_cloud=&sender=cmmp_sv_100017 200 35ms 58b
2020-03-19 17:22:43 +08:00: 1