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This chapter delves into the fundamentals of FTP (File Transfer Protocol) and its practical applications for transferring files over networks. It covers key aspects including FTP clients, anonymous login, binary vs ASCII transfer modes, and the popular vsftpd server setup on Fedora. You'll learn about essential FTP commands, security considerations, and configuration details to successfully manage FTP connections and ensure secure file transfers. This guide is perfect for both beginners and experienced users looking to enhance their knowledge of FTP and vsftpd.
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Chapter 19 FTP: Transferring Files Across a Network • FTP Client • JumpStart: Downloading Files Using fip Notes • Anonymous FTP • Automatic Login • Binary versus ASCII Transfer Mode • ftp Specifics • FTP Server (vsftpd) • JumpStart: Starting a vsftpd Server • Testing the Setup • vsftpd.conf: Configuring vsftpd
Introduction • ftp has been around as one of the original TCP/IP protocols • ftp and vsftpd – this chapter will focus more on vsftpd since it is provided with Fedora • Security – vsftp is secure, ftp is not • Connections – passive is client initiated connection, active is if server initiates
FTP Client • ftp – command line, Linux or Windows • sftp – secure ftp, part of OpenSSH • gftp – graphical ftp, supports ftp, SSH, and HTTP • ncftp – Fedora text-based utility with more features than standard ftp
]umpStart: Downloading Files Using ftp • Basic commands: • ftp ftp.server.net • ftp> open ftp.server.net • ftp> user • ftp> get (mget) • ftp> put (mput) • ftp> prompt • ftp> hash • ftp> ascii or binary • ftp> cd and lcd • ftp> quit or bye
Anonymous FTP • Can use user id of either • anonymous or • ftp (some systems) • Enter email address as password if necessary, see automatic login below • ftp server can use reverse DNS to verify
Automatic Login • Place ~/.netrc file in your home directory to allow automatic login: $ cat .netrc machine bravo login jimbo password xyz123 • Make readable only by owner! • Can defeat at ftp server config file
Binary versus ASCII Transfer Mode • Binary mode (default for some systems) provides a byte by byte exact transfer • ASCII (ascii) mode converts end of line characters between Windows and Unix systems • Can also use dos2unix or unix2dos • Security – always use binary mode
ftp Specifics • Format – ftp [-options] server • Options: • -i interactive • -g globbing, file name expansion with wild cards • -v verbose • -n no automatic login with .netrc
ftp commands • Shell command = !command (!ls) • Transfer files: • append local remote • get remote-file [new local file name] • mget remote-file-list [wild cards allowed] • put local-file [new remote file name] • mput remote-file-list [wild cards allowed] • newer remote-file [new local file name] • reget remote-file [new local file name]
status • ascii – sets transfer mode to ASCII • binary – sets transfer mode to binary • close – quits ftp server without leaving ftp • open [server name] – opens new ftp connection • hash – shows hash marks (#) during transfers • prompt – toggles prompts for transfers • passive – toggles between passive and active • user – sign in as different user • quit or bye – exits ftp site and closes ftp
Directories • cd - changes directories on ftp server/site • lcd – changes local directories on your machine • Do not use ftp> ! cd newdirectory • Remember that the environment does not change in a spawned process!
Files • chmod – to change permissions on files • delete – to delete remote file(s) if allowed • mdelete remote-file-list
Display Information • dir – like ls but has file option: • dir [remote-dir] file • (file saved on your local system with contents of the remote directory listing) • ls – same as dir but with more information • help – shows commands • pwd – print working remote directory • status – status information • verbose – to see all that is happening
FTP Server (vsftpd) • The vsftpd package is installed by default on Red Hat systems • Modes: • Standalone – set listen parameter to “yes” in vsftpd.conf file • Normal – use xinetd superserver to start and stop, set to normal by default
JumpStart: Starting a vsftpd Server • Make sure service is running: # /sbin/service vsftpd status vsftpd (pid 3022) is running . . . • Check permissions in /var/ftp directory # ls –ld /var/ftp drwxr-xr-x 4 root root 4096 Aug 12 /var/ftp
vsftpd.conf: Configuring vsftpd • Standalone – listen=yes • listen_port (default 21) • listen_address – defaults to any network interface • max_clients – set to 0 for unlimited • max_per_ip – set to 0 for any IP address allowed
Logging in • userlist_enable – yes further checks userlist_deny, no does not check the list, more secure is no • userlist_deny – list of users denied access • userlist_file – name of user list file • local_enable – allows users in /etc/passwd file to log onto system
Anonymous Users • anonymous_enable – yes allows anonymous • no_anon_password – yes won’t ask for password • deny_email_enable – yes checks if email password user is denied access to system • banned_email_file – list of denied users by email address
Working Directories and chroot jail • chroot_list_enable – sets user in jail either in their home directory or in /var/ftp • chroot_local_user – if set to no local user can move around directory structure • chroot_list_file – naem of the file if chroot_list_file is set to yes • passwd_chroot_enable – allows local user to cd to home directory (/home/./jones) • secure_chroot_dir – empty directory that is not writeable by user ftp, a secure chroot jail
Messages • dirmessage_enable – yes displays .message • banner_file – file that is displayed at login, overrides ftpd_banner • ftpd_banner – overrides the standard vsftpd greeting banner at connection time • And speaking of banners:
