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FTP server says: "421 service not available, remote server has closed connection."

If an FTP server won't allow logins, it is probably configured
correctly, but the problem is probably with authorizing users at
login. FTP servers in current distriubtions often authorize users with
the Pluggable Authentication Modules library, in which case there
should be an authorization file /etc/pam.d/ftp. A generic
authorization file looks like this. (The line break on the first
"auth" line is for readability. The entry is actually a single, long
line).

#%PAM-1.0
auth required /lib/security/pam_listfile.so item=user \
sense=deny file=/etc/ftpusers onerr=succeed
auth required /lib/security/pam_pwdb.so shadow nullok
auth required /lib/security/pam_shells.so
account required /lib/security/pam_pwdb.so
session required /lib/security/pam_pwdb.so

Also, make sure the /etc/ftpusers file, or whatever users file is
named in the first "auth" line, is configured correctly.

Btw, the sample ftp file above is actually theftpd/ftp.pam.sample file
from the ftpd-BSD-0.3.1.tar.gz package. Many thanks to David A. Madore
for this much needed port.

10. The X Window System

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