如何让 tcpsvd 放弃其 root 权限？

Question

假设脚本在启动时以 root 身份运行。我想从这个脚本开始tcpsvd -E 0 515 lpd。我想tcpsvd以非特权用户身份运行。但它需要 root 权限才能绑定到端口 515。我该如何实现这一点？

此外我必须使用busybox tcpsvd：

tcpsvd
tcpsvd [-hEv] [-c N] [-C N[:MSG]] [-b N] [-u USER] [-l NAME] IP PORT PROG

Create TCP socket, bind to IP:PORT and listen for incoming connection.
Run PROG for each connection.

    IP              IP to listen on. '0' = all
    PORT            Port to listen on
    PROG [ARGS]     Program to run
    -l NAME         Local hostname (else looks up local hostname in DNS)
    -u USER[:GRP]   Change to user/group after bind
    -c N            Handle up to N connections simultaneously
    -b N            Allow a backlog of approximately N TCP SYNs
    -C N[:MSG]      Allow only up to N connections from the same IP
                    New connections from this IP address are closed
                    immediately. MSG is written to the peer before close
    -h              Look up peer's hostname
    -E              Do not set up environment variables
    -v              Verbose

Answer 1

您需要在以 root 身份运行时将程序绑定到端口，然后切换到非特权用户。 tcpsvd提供-u执行此操作的选项：

 -u user[:group]
          drop permissions.  Switch user ID to user’s UID, and group ID to
          user’s primary GID after creating and binding to the socket.  If
          user  is  followed  by a colon and a group name, the group ID is
          switched to the GID of group instead.  All supplementary  groups
          are removed.