性能检测命令
top
free
df
uptime
last
history
vmstat 1
sar
iostat
netstat -an
nmap -sT -O localhost
uname -r
chkconfig --list
w
du -ms
netstat -n -p -t | grep SYN_RECV | grep :80 | wc -l
ps -aux | grep imap
killall imapd
less /etc/sysconfig/iptables
less /etc/ssh/sshd_config
less /etc/passwd //look for new user
less /etc/group //look for new group or if have new user in root group
less /etc/rc.d/rc.local
Monitor Opening Port
# nmap –sT –O localhost
834/tcp open unknown
# cat /etc/services | grep 834 //查看834端口是否和任何已知服务相关
# netstat –anp | grep 834 //p选项揭示了打开834端口的进程ID（PID）
# lsof –i | grep 834
查找或删除正在使用某文件的进程
fuser filename
fuser -k filename
yum clear all
yum -y update
if you find "Error: Cannot find a valid baseurl for repo", try to ping 