would you help me how i can connect a unix server and send a command using .net
for example changing chmod of a file?
Unfortunately there is no usefull information about this on net. But i want to do this using ftp server(not domain name or ip address)

There are lots of mechanisms for connecting to a Unix server. What kind of connection do you want to establish? FTP, SFTP, Telnet, SSH, NFS, SAMBA file access, SSHFS, etc. Each protocol behaves a little differently.

thanks for your reply .i need FTP connection. For instance sending command to change file permission(chmod). But it must be logged in by ftp credentials.

First and foremost, it will depend on whether or not the remote server supports chmod as an FTP command. If not, you are sunk before you start. Log into the FTP server in question using an FTP program and see if chmod is in the list. If not look for shell, which gives you access to a restricted shell on the remote system; most servers do not implement shell because of the problems it can let happen.

In VB.Net, look at Net.FtpWebRequest in the help system for info on connecting with FTP servers.