How do you know if a file has been modified on an FTP server?
Also applies to the following FTP FAQs:
Q: My FTP server doesn't support MDTM, MFMT, or SITE UTIME. How do I use the files modification date & time?
Q: My FTP server returns the wrong file size. How will this affect SyncBack?
Q: Can SyncBack be used with my FTP server?
Answer
SyncBack uses three methods to check if a file has been modified: its last modification date & time, its size, and its hash value (MD5 or CRC32).
Some FTP servers can accurately return the files last modification date & time (using the MDTM or MLST command), and some (very few) allow the caller to set the date & time (again using the MDTM command, MFMT, or SITE UTIME). Worse still, some FTP servers do not return the correct file size (it can be rounded up or down to the nearest block size, with the block size unknown to the user). For this reason, SyncBack may not work correctly with your FTP server. The best FTP server to use is one that supports both getting & setting the files modification date & time and accurately returns file sizes. SyncBack will try its best to work with your FTP server, but it is impossible to support all FTP servers.
SyncBackFree does not support the MLST command.
SyncBack Touch
An alternative to using FTP is to use SyncBack Touch. SyncBack Touch is a cross-platform file server. It lets SyncBackPro and SyncBackSE copy files to and from another device, e.g. Windows, macOS, Linux or Android device, over the network (LAN or Internet) just like an FTP server. SyncBackFree cannot use SyncBack Touch.
Simply install SyncBack Touch on the device you want to the access the files on and then create a profile in SyncBackPro/SE to use that device.
The advantages to using SyncBack Touch instead of FTP are that you can copy open/locked files, it's far simpler to set-up, doesn't have all the compatibility problems of FTP (e.g. does it support MDTM or MFMT?) and doesn't require complex firewall/router configuration.