## ProFTPD module `mod_xfer`

The `mod_xfer` module handles most of the FTP commands related to file transfers.

## Directives

- AllowOverwrite
- AllowRetrieveRestart
- AllowStoreRestart
- DeleteAbortedStores
- DisplayFileTransfer
- HiddenStores
- MaxRetrieveFileSize
- MaxStoreFileSize
- MaxTransfersPerHost
- MaxTransfersPerUser
- StoreUniquePrefix
- TimeoutNoTransfer
- TimeoutStalled
- TransferPriority
- TransferRate
- UseSendfile

## MaxRetrieveFileSize

Syntax: MaxRetrieveFileSize [number|"*" units ["user"|"group"|"class" expression]] Default: None
Context: server config, `<VirtualHost>`, `<Global>`, `<Anonymous>`, `<Directory>`, `.ftpaccess`
Module: mod_xfer
Compatibility: 1.2.7rc1 and later

The `MaxRetrieveFileSize` directive sets a maximum limit on the size of a single file downloaded from `proftpd`. If the requested file size is larger than than the configured maximum limit, the data transfer will be rejected.

A single "*" argument configures unlimited file sizes, and is used primarily to override any inherited restrictions from higher-level configuration sections. The given number is the number of bytes for the limit, and is followed by a units specifier of (case-insensitive) "Gb" (Gigabytes), "Mb" (Megabytes), "Kb" (Kilobytes), or "B" (bytes). The given number of bytes is multiplied by the appropriate factor.

The optional parameters are used to restrict the file size limits only to specific users. If the "user" restriction is given, then expression is a user-expression specifying to which users the rule applies. Similarly for the "group" restriction. For the "class" restriction, the expression is simply the name of connection class for whom the rule will apply. If no matching user, group, or class expression (in that order) is found for the current user, then a limit with no expression (i.e. no "user", "group", or "class" identifier) is applied.

Examples: # Restrict downloads to only 1 gigabyte MaxRetrieveFileSize 1 Gb # Restrict downloads for user fred, but allow unlimited download size for # everyone else MaxRetrieveFileSize 50 Kb user fred MaxRetrieveFileSize *

See also: `MaxStoreFileSize`

## MaxStoreFileSize

Syntax: MaxStoreFileSize [number|"*" units ["user"|"group"|"class" expression]] Default: None
Context: server config, `<VirtualHost>`, `<Global>`, `<Anonymous>`, `<Directory>`, `.ftpaccess`
Module: mod_xfer
Compatibility: 1.2.7rc1 and later

The `MaxStoreFileSize` directive sets a maximum limit on the size of a single file uploaded to `proftpd`. When the configured maximum limit is reached, the data transfer will be aborted.

A single "*" argument configures unlimited file sizes, and is used primarily to override any inherited restrictions from higher-level configuration sections. The given number is the number of bytes for the limit, and is followed by a units specifier of (case-insensitive) "Gb" (Gigabytes), "Mb" (Megabytes), "Kb" (Kilobytes), or "B" (bytes). The given number of bytes is multiplied by the appropriate factor.

The optional parameters are used to restrict the file size limits only to specific users. If the "user" restriction is given, then expression is a user-expression specifying to which users the rule applies. Similarly for the "group" restriction. For the "class" restriction, the expression is simply the name of connection class for whom the rule will apply. If no matching user, group, or class expression (in that order) is found for the current user, then a limit with no expression (i.e. no "user", "group", or "class" identifier) is applied.

Examples:

      # Restrict upload to only 3 megabytes
      MaxStoreFileSize 3 Mb

      # Restrict anonymous uploads to 50k, but allow unlimited upload size for
      # everyone else
      MaxStoreFileSize 50 Kb user anonymous
      MaxStoreFileSize *

NOTE: In FTP uploads, the size of the file being uploaded is not sent to the FTP server first; this means that the FTP server does not know in advance how much data the FTP client is going to send. The FTP server can only count the number of bytes being uploaded, and stop the transfer when a configured limit is reached. This means that `MaxStoreFileSize` cannot be used to prevent an FTP client from even sending the bytes over the network.

See also: `MaxRetrieveFileSize`

## TransferPriority

Syntax: TransferPriority cmd-list "low"|"medium"|"high"|number
Default: None
Context: server config, `<VirtualHost>`, `<Global>`, `<Anonymous>`
Module: mod_xfer
Compatibility: 1.3.2rc1 and later

The `TransferPriority` directive is used to tweak the process priority (a la `nice(1)`) of the session during data transfers. For example, large (or anonymous) data transfers can be configured to have lower priorities, so as to get lower priority than other applications from the kernel.

The priority parameter can one of the convenient "high", "medium", or "low" keywords, or it can be an explicit number. As per the `nice(1)` man page, the higher the number, the lower the priority; the highest priority is -20, and the lower priority is 19.

Examples:

      # All data transfers get a low priority
      TransferPriority APPE,RETR,STOR low

Or maybe only downloads should have lower priorities, but uploads should be fine:

      TransferPriority RETR low

## TransferRate

Syntax: TransferRate cmd-list kbytes-per-sec[:free-bytes]
Default: None
Context: server config, `<VirtualHost>`, `<Global>`, `<Anonymous>`, `<Directory>`, .ftpaccess
Module: mod_xfer
Compatibility: 1.2.8rc1 and later

The `TransferRate` directive is used to set transfer rate limits on the transfer of data. This directive allows for transfer rates to be set in a wide variety of contexts, on a per-command basis, and for certain subsets of users (via `mod_ifsession`). Note that these limits only apply to an individual session, and do not apply to the overall transfer rate of the entire daemon.

The cmd-list parameter may be an comma-separated list of any of the following commands: `APPE`, `RETR`, `STOR`, and `STOU`.

The kbytes-per-sec parameter is the actual transfer rate to be applied.

The free-bytes parameter, if configured, allows that number of bytes to be transferred before the rate limit is applied. This allows for clients transferring small files to be unthrottled, but for larger files, such as MP3s and ISO images, to be throttled.

Here are some examples:

      # Limit downloads for everyone
      TransferRate RETR 1.5

      # Limit uploads (and appends!) to the prolific users in the
      # lotsofuploadfiles.net domain. This presumes that a Class has been defined
      # for that domain, and that that Class has been named "uploaders". Let them
      # upload small files without throttling, though.

      <IfClass uploaders>
        TransferRate APPE,STOR 8.0:1024
      </IfClass>

## UseSendfile

Syntax: UseSendfile on|off|len units|percentage
Default: None
Context: server config, `<VirtualHost>`, `<Global>`, `<Anonymous>`, `<Directory>`, .ftpaccess
Module: mod_xfer
Compatibility: 1.3.0rc1 and later

The `UseSendfile` directive controls use of `sendfile(2)` functionality, which is an optimization for sending files to clients. Use of `sendfile(2)` functionality avoids separate read and send kernel operations, and buffer allocations. Read this howto for more details.

## Installation

The `mod_xfer`module is always installed.

Author: $Author: castaglia $
Last Updated: $Date: 2011/04/26 16:10:11 $

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