Chattr is a Linux utility that allows you to change file and directory attributes. Normally you would use it to change files so that they cannot be easily damaged or overwritten. However you may find yourself needed a tool like this if you have had a rootkit installed on a Linux server. One of the “tricks” the script kiddies use is to set some of the attributes of files and folders so that normal commands like mv and rm fail. In this case you would check using the lsattr command to see if any of the bits are set. Then you could use chattr -suSadAc filename followed by chattr -i filename before trying to remove them again.
Warning : if you have a rootkit – do not assume that the lsattr and chattr (and pretty much all the common binaries) have not been compromised. Use a known rootkit free set of tools !!