Network-manger is not removed.
the format of file is correctly as you mentioned.
after write :
sudo ifdown wlan0 && sudo ifup wlan0
but when type :
ifdown: interface wlan0 not configured
ifup: interface wlan0 already configured
The end of command run is :
No DHCPOFFERS received.
Trying recorded lease 192.168.1.100
PING 192.168.1.1 (192.168.1.1) 56(84) bytes of data.
--- 192.168.1.1 ping statistics ---
1 packets transmitted, 0 received, +1 errors, 100% packet loss, time 0ms
No working leases in persistent database - sleeping.