【求助】请教高手：启动l2tpd后，连接vpn时出错

baifjtnog

启动l2tpd后

echo "c aaa">/var/run/l2tp-control

在连接时说是

getPtyMaster: No more free pseudo-tty's
start_pppd: unable to allocate pty, abandoning!
write_packet: tty is not open yet.
check_control: control, cid = 0, Ns = 2, Nr = 4
write_packet: tty is not open yet.
write_packet: tty is not open yet.
是怎么回事（关tty小弟不懂），谢谢