maximum ftp users

[Dan Copeland]

Is there a limit on the number users that can do ftp to a server at any point of time? If so what is it and how can we manually tweak it

Please advise

[Stephen Keane]

You are going to be limited by the number of open files per process (nfile) for the ftp process(es) (treating each socket as a file), also bandwith on your NIC and available ports. Off the top of my head, that's all I can think of.

[Uday_S_Ankolekar]

If you want to control ftp to any specific users , like number of sessions, time based ftp then you need to edit/create ftpaccess file

man ftpaccess for more information.

-USA..

[rick jones]

nfile is indeed one limit - it is though the _system_wide_ open file limit not the per-process (maxfiles/maxfiles_lim). Last I remember checking, an ftpd process consumed O(8) file descriptors.

Each ftp session is also a distinct process, so there will be a limit at the maximum number of processes - nproc.

Of course, CPU utilization and RAM consumption will come into play, as well as network bandwidth available to the host.

The writeups are a bit old, so the constants may not be "right" but the ideas still hold, so the "ftp" and/or software download writeups at:

ftp://ftp.cup.hp.com/dist/networking/briefs/

may be of some use.

[Biswajit Tripathy]

Rick pretty much explained the system limits on FTP
at any point of time, so I will not go into that.

When you say "manually tweak" the limit, what do
you exactly mean? If you want to control the
number of incoming FTP sessions on your server
(like, for ex, you want to allow only 100 FTP
sessions at any point of time and no more), then
you could use IPFilter to achieve that. If that's what
you want, then configure the IPFilter with following
options and rules:

1) Execute the following command:
$ /sbin/ipf -m e

The above command should say "DCA MODE is
enabled"

2) Configure the following rule:

$ /sbin/ipf -f -
pass in quick proto tcp from any to any port = 21 keep limit 100 cumulative

The above configuration will allow only 100 incoming
FTP connections and will block any connection
beyond that. New FTP connections will only be
allowed when older connection closes.

- Biswajit