Useful Tips for Linux

• SSH tunnelling
• SSH reverse tunneling
• USB key
• How to save an audio/video stream to a file in your hard-disk

SSH tunnelling is an interesting way to tunnel clear text protocols through a secure communication channel.

To tunnel POP3 traffic using ssh you should create a local ssh tunnel on your local machine (using port 1234, for instance) to the remote mail server port 110.

$ ssh -f -L 1234:localhost:110 user@remoteserver tail -f /dev/null

the command tail -f /dev/null is used to fork the process

Configure your mail client to access your mail via POP3, using localhost and port 1234

SSH reverse tunneling allows to bypass a firewall.

At the firewalled machine (incoming ports only) use:

$ ssh -R 2048:localhost:22 remoteclient

At the other end:

$ ssh -p 2048 localhost

To make an USB Memory Key work under Linux (kernel 2.4), you need to make sure that all the following modules are loaded into the kernel (using modprobe):

• /sbin/modprobe usbcore
• /sbin/modprobe usb-uhci (or usb-ohci)
• /sbin/modprobe usb-storage
• /sbin/modprobe scsi_mod
• /sbin/modprobe sg
• /sbin/modprobe sd_mod

Mount the key (usually it apperas as a scsi device) using:

$ mount -t vfat /dev/sda1 /mnt/usbkey

A Realplayer or WindowsMedia audio/video stream can be saved in a file on your hard-disk, just use mplayer with the option -dumpstream:

mplayer -dumpstream rtsp://whatever/stream.rm