In our IIS FTP log we have an entry that includes this:
[26]USER
Where can I look up to see the meaning of this? Particularly the number in the square brackets?
It appears
That'll teach me to post before properly looking :-)
More information would be VERY useful: Which operating system are you running? Which ftp daemon are you running?
If you are on a Linux with a rpm based package manager you could try something like
rpm -qa | grep -i ftp
to find out which ftp packages you have installed.
Read the man page and or web page of the ftp daemon in use.
You can have a look at the Wikipedia Article about FTP to learn the basics of the protocol. Fort further information you can have a look the documentation of the File Transfer Protocol.
FTP is dialog based, which means that the server and client are sending in turns information and answers to requests. USER <username>
is the command for authenticating at the server with the given username.