[Linux]常用命令

1.观察程序运行时，调用了哪些东西

 $ strace test
  execve("test", ["test"], [/* 26 vars */]) = 0
  [..]
  open("/lib/libc.so.6", O_RDONLY)        = 3
  [..]
  socket(PF_INET, SOCK_STREAM, IPPROTO_TCP) = 3
  getsockopt(3, SOL_SOCKET, SO_KEEPALIVE, [0], [4]) = 0
  close(3)                                = 0
  [..]
  _exit(0)                                = ?

2. 输出上一条命令的执行结果 echo $?

3. ubuntu 启用  root  : sudo passwd root

                  禁用 root  : sudo passwd -l root