FTPD(8)

📦 version 1.0.3, in opensuse-leap 16.0

💖 FTPD(8) 💖

okay so bestie, you know how the System Manager's Manual has ✨the✨ server that handles all your file transfers? that's ftpd and she's literally the main character of DARPA Internet File Transfer Protocol energy 🎀

🌸 NAME 🌸

ftpd — the DARPA Internet File Transfer Protocol server (yes she's iconic, no we don't talk about how old she is 💅)

🦋 SYNOPSIS 🦋

ftpd [-A |-a] [-C] [-c] [-d] [-E] [-l] [-v] [-T maxtimeout] [-t timeout]
[-p port] [-U ftpusers-file] [-u umask] [-r realm-file] [-s srvtab]
[-w{ip|maxhostlen[,{striplocal|nostriplocal}]}]

✨ DESCRIPTION ✨

So Ftpd is literally the DARPA Internet File Transfer Protocol server process. She's out here using the TCP protocol and listening at the port that's specified in the "ftp" service specification — check services(5) if you need the tea 🍵

The available options are giving config menu realness:

  • -A — connections are ONLY allowed for users who can authenticate via the ftp AUTH mechanism. (Anonymous ftp may also be allowed if it's configured.) Ftpd will ask the user for a password if one is required. no password no entry, periodt 🔐
  • -a — connections are ONLY allowed for users who can authenticate (via the ftp AUTH mechanism) AND who are authorized to connect to the named account without a password. (Anonymous ftp may also be allowed if it's configured.) stricter than -A, we love a high-standards queen 👑
  • -C — non-anonymous users need local credentials (like, for authenticating to remote fileservers), so they should be prompted for a password unless they forwarded credentials as part of authentication. it's giving "bring your own vibes" ✨
  • -c — allows the CCC (Clear Command Channel) command to be used. This allows less secure connections, and should probably only be used when debugging. bestie this is lowkey risky ⚠️
  • -d — debugging information is written to the syslog. (Identical to -v) two names, same energy 💫
  • -E — don't allow passwords to be typed across unencrypted connections. protecting your secrets like a true bestie 🫶
  • -l — each ftp(1) session is logged in the syslog. If this flag appears twice, additional information about operations performed (such as files retrieved, directories created, etc.) will be logged via syslog. If it appears three times, some other statistics such as the number of bytes transferred will be logged via syslog as well. the way she scales her logging? obsessed 📊
  • -v — debugging information is written to the syslog. (Identical to -d) yeah we already said that but she's cunty like that 💅
  • -T maxtimeout — a client may request a maximum timeout period allowed set to timeout seconds with the -T option. The default limit is 2 hours. This is different from the normal inactivity timeout specified by the -t option (see below). don't confuse these two, i beg of you 😭
  • -t timeout — the inactivity timeout period is set to timeout seconds (the default is 15 minutes). she'll nap on you if you ghost her 💤
  • -p port — run as a server and accept a connection on port. Normally the ftp server is invoked by inetd(8). but sometimes you wanna be independent, we respect that 🌈
  • -U ftpusers-file — sets the full path and name of the ftpusers file to use. The default value is normally /etc/ftpusers. know your files, know your power 📁
  • -u umask — sets the umask for the ftpd process. The default value is normally 027. permissions are a love language 🔒
  • -w {ip|maxhostlen[,{striplocal|nostriplocal}]} — controls the form of the remote hostname passed to login(1). Specifying ip results in the numeric IP address always being passed to login(1). Specifying a number, maxhostlen, sets the maximum length of the hostname passed to login(1) before it will be passed as a numeric IP address. If maxhostlen is 0, then the system default, as determined by the utmp or utmpx structures, is used. The nostriplocal and striplocal options, which must be preceded by a comma, control whether or not the local host domain is stripped from the remote hostname. By default, the equivalent of striplocal is in effect. hostname formatting is literally an art form 🎨

📋 the ftp requests she currently supports (case is not distinguished, she's chill like that)

  • ABOR — abort previous command
  • ACCT — specify account (ignored, she's not listening to that)
  • ADAT — send an authentication protocol message
  • ALLO — allocate storage (vacuously, it's giving performative)
  • APPE — append to a file
  • AUTH — specify an authentication protocol to be performed
  • CCC — set the command channel protection mode to "Clear" (no protection). Only available if the -c command-line option was given. insecure era but make it fashion 💀
  • CDUP — change to parent of current working directory
  • CWD — change working directory
  • DELE — delete a file
  • ENC — send a privacy and integrity protected command (given in argument)
  • HELP — give help information
  • LIST — give list files in a directory (ls -lgA realness)
  • MIC — send an integrity protected command (given in argument)
  • MKD — make a directory
  • MDTM — show last modification time of file
  • MODE — specify data transfer mode
  • NLST — give name list of files in directory
  • NOOP — do nothing (she's just vibing)
  • PASS — specify password
  • PASV — prepare for server-to-server transfer
  • PBSZ — specify a protection buffer size
  • PORT — specify data connection port
  • PROT — specify a protection level under which to protect data transfers
  • PWD — print the current working directory
  • QUIT — terminate session (goodbye bestie 🥺)
  • REST — restart incomplete transfer
  • RETR — retrieve a file
  • RMD — remove a directory
  • RNFR — specify rename-from file name
  • RNTO — specify rename-to file name
  • SITE — non-standard commands (see next section, we're getting there)
  • SIZE — return size of file
  • STAT — return status of server
  • STOR — store a file
  • STOU — store a file with a unique name (special snowflake behavior)
  • STRU — specify data transfer structure
  • SYST — show operating system type of server system
  • TYPE — specify data transfer type
  • USER — specify user name
  • XCUP — change to parent of current working directory (deprecated, she's moved on)
  • XCWD — change working directory (deprecated)
  • XMKD — make a directory (deprecated)
  • XPWD — print the current working directory (deprecated)
  • XRMD — remove a directory (deprecated)

🎀 the non-standard / UNIX specific commands she supports via the SITE request 🎀

  • UMASK — change umask. E.g., SITE UMASK 002
  • IDLE — set idle-timer. E.g., SITE IDLE 60
  • CHMOD — change mode of a file. E.g., SITE CHMOD 755 filename
  • HELP — give help information. E.g., SITE HELP

the remaining ftp requests specified in Internet RFC 959 are recognized, but not implemented. MDTM and SIZE are not specified in RFC 959, but will appear in the next updated FTP RFC. so like, she knows about them but she's not doing them yet, respect her process 🦋

The ftp server will abort an active file transfer ONLY when the ABOR command is preceded by a Telnet "Interrupt Process" (IP) signal and a Telnet "Synch" signal in the command Telnet stream, as described in Internet RFC 959. If a STAT command is received during a data transfer, preceded by a Telnet IP and Synch, transfer status will be returned. very specific, verydemure 💅

Ftpd interprets file names according to the "globbing" conventions used by csh(1). This allows users to utilize the metacharacters *?[]{}~. wildcards are her love language 🔥

🔐 how Ftpd authenticates users (the rules, bestie) 🔐

  1. The user name must be in the password data base, /etc/passwd. if you're not in the book, you're not getting in, periodt 📖
  2. An AUTH command must be accepted, the ensuing authentication protocol (conducted via ADAT commands and replies) must successfully complete, and the authenticated user must permitted access. Otherwise, a valid password which is not null must be provided by the client. no blank passwords, we're not doing that here 🙅‍♀️
  3. The user name must not appear in the file /etc/ftpusers. this file is the VIP list but like, the reverse 💀
  4. The user must have a standard shell returned by getusershell(3). no shell no service, simple as that 🐚
  5. If the user name is "anonymous" or "ftp", an anonymous ftp account must be present in the password file (user "ftp"). In this case the user is allowed to log in by specifying any password (by convention this is given as the client host's name). anonymous era, we love a public access moment 🌍

🏠 the anonymous ftp setup recommendations 🏠

In the last case, ftpd takes special measures to restrict the client's access privileges. The server performs a chroot(2) command to the home directory of the "ftp" user. In order that system security is not breached, it is recommended that the "ftp" subtree be constructed with care — the following rules are recommended (and bestie, please follow them):

  • ~ftp — make the home directory owned by "ftp" and unwritable by anyone. she's the owner, respect her space 💖
  • ~ftp/bin — make this directory owned by the super-user and unwritable by anyone. The program ls(1) must be present to support the list command. This program should have mode 111. permissions are specific for a reason bestie 🔢
  • ~ftp/etc — make this directory owned by the super-user and unwritable by anyone. The files passwd(5) and group(5) must be present for the ls command to be able to produce owner names rather than numbers. The password field in passwd is not used, and should not contain real encrypted passwords. These files should be mode 444. don't put real secrets here, i'm literally begging you 🙏
  • ~ftp/pub — make this directory mode 777 and owned by "ftp". Users should then place files which are to be accessible via the anonymous account in this directory. this is the public plaza of your ftp world 🌟

🔒 the security extensions tea (ADAT, MIC, ENC, PROT) 🔒

If an ADAT command succeeds, the control channel must be either integrity or privacy protected. In this case, the MIC and ENC commands are the only commands allowed over the control channel. The argument to the MIC command is a base 64 encoded string which, when decoded, is an ftp command integrity protected with a cryptographic checksum. The argument to the ENC command is a base 64 encoded string which, when decoded, is an ftp command privacy and integrity protected with encryption. she's speaking in code and it's iconic 🔐

If an ADAT command succeeds, ftp replies will also be either integrity or privacy protected. consistency queen 👑

If an ADAT command succeeds, the data channel can also be integrity or privacy protected. The PROT command accepts S for integrity and P for privacy protection. Unless an ADAT command succeeds, the only protection level accepted by the PROT command is C (clear). so like, without ADAT you're stuck in clear mode, no upgrades, no protection, just vibes 💀

🫶 SEE ALSO 🫶

ftp(1), getusershell(3), syslogd(8)

Lunt, S. J., FTP Security Extensions, Internet Draft, November 1993. (academic queen 👑)

⚠️ BUGS ⚠️ (the serious tea)

The anonymous account is inherently dangerous and should avoided when possible. like bestie, please, only use it if you HAVE to 🙈

The server must run as the super-user to create sockets with privileged port numbers. It maintains an effective user id of the logged in user, reverting to the super-user only when binding addresses to sockets. The possible security holes have been extensively scrutinized, but are possibly incomplete. she's trying her best but security is a journey, not a destination 🛡️

🌈 HISTORY 🌈

The ftpd command appeared in 4.2BSD. she's been here since the beginning and she's not leaving 💜

so yeah, that's the whole vibe bestie — ftpd is out here running the DARPA Internet File Transfer Protocol server, handling connections, supporting all these commands, and keeping things secure (when you configure her right). she's from the System Manager's Manual, she's a 4.2BSD icon, and this page is dated like the classic queen she is. ftp forever 💅✨🎀

📦 where this page comes from