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ProFTPD: Logging
ProFTPD: Logging
Logging
Logging the activity of the server is an integral part of effective server
administration. ProFTPD provides several different and flexing logging
mechanisms. When examining the different logging mechanisms, have in
mind the intended use of the logged data, the volume of data being logged,
any post-processing that may need to be done, etc. Log files are more
useful when they contain a complete record of server activity. It is often
easier to simply post-process the log files to remove requests that you do not
want to consider.
Security Warning
Anyone who can write to the directory where ProFTPD is writing a log file can
almost certainly gain access to the UID that the server is started under, which
is normally root . Do not give people write access to the
directory where the logs are stored without being aware of the consequences:
if the logs directory is writable (by a non-root user), someone
could replace a log file with a symlink to some other system file, and then
root might overwrite that file with arbitrary data. If the log
files themselves are writable (by a non-root user), then someone
may be able to overwrite the log itself with bogus data.
When opening log files, proftpd will by default log a warning if
the file being opened for logging is in a directory that does not exist, or
is world-writable. The log file will not be written in world-writable
directories; there are no exceptions. (If you have configured log files in
your proftpd.conf that are not appearing, check for the warnings
about world-writable directories.) The proftpd process will also,
by default, log a warning if the file given is a symlink; this symlink check
can be configured via the AllowLogSymlinks directive.
In addition, log files may contain information supplied directly by the client,
without escaping. Therefore, it is possible for malicious clients to insert
control-characters in the log files, so care must be taken in dealing with
raw logs.
Unix syslog Logging
By default, proftpd will log via syslog(3) , using
the daemon facility (auth for some logging),
at various levels: err , notice , warn ,
info , and debug (debugging is done at this syslog
level). The location of the server's log files in this case is determined by
your /etc/syslog.conf configuration.
You can fine-tune your proftpd 's syslog-based logging via the
SyslogFacility and SyslogLevel directives. See the log level documentation for
more details on these settings.
Log Files
There are three main types of logs that a proftpd daemon can
generate: TransferLog , SystemLog , and
ExtendedLog .
TransferLog
A TransferLog
is the most common log kept, recording file transfers. It is written in the
xferlog(5) format, described here, and in the
xferlog(5) man page.
Each entry in the TransferLog is a single line of space-delimited
fields:
Field |
Values |
Description |
current-time |
DDD MMM dd hh:mm:ss YYYY |
Current local time at the time of transfer |
transfer-time |
Seconds |
Total time in seconds for the transfer |
remote-host |
String |
Remote client DNS name (or IP address) |
file-size |
Bytes |
Number of bytes transferred |
filename |
String |
Name of the transferred file |
transfer-type |
Flags |
Indicates whether the transfer was an ASCII ("a" ) or
binary ("b" ) transfer |
special-action-flag |
Flags |
One or more single character indicating any special action taken: "C" (compressed), "U" (uncompressed), "T" (tarred), "_" (no action) |
direction |
Flags |
Direction of the transfer: "o" (outgoing, i.e. download), "i" (incoming, i.e. upload), "d" (deleted) |
access-mode |
Flags |
Method by which the user is logged in: "a" (anonymous), "g" (guest), "r" (real user) |
username |
String |
Authenticated username |
service-name |
String |
Name of the service used: "ftp", "sftp", "scp", etc |
authentication-method |
Flags |
Method of authentication used: "0" (none), "1" (RFC 1413) |
authenticated-user-id |
Flags |
Name of user provided by RFC 1413 lookup, otherwise "*" |
completion-status |
Flags |
Single character indicating the status of the transfer: "c" (complete), "i" (incomplete) |
History of the xferlog(5) Format
This xferlog(5) format seems a bit odd, right? To understand this, it helps
to keep in mind the history of this format. The xferlog(5) format
predates ProFTPD. The ProFTPD Project copied this format from
wu-ftpd, which
was the popular FTP server at that time. There were already existing
tools/scripts which knew how to parse that format, so ProFTPD used it. Since
then, wu-ftpd has waned in maintenance and popularity; other
FTP servers (e.g. pure-ftpd , vsftpd , but
not the built-in ftpd on FreeBSD) have since then picked
up the xferlog(5) format from ProFTPD. Thus this log format has
a 20+ year history, and keeps going.
This history helps explain certain fields in the xferlog(5)
format, such as the authentication-method and
authenticated-user-id fields. These fields were more relevant in
the past, when the RFC 1413 Identd protocol was more widespread in use. Now,
very few sites run identd servers; these fields in the
log format are thus archaic. Thus in almost all ProFTPD-generated
TransferLog entries, authentication-method will be "0",
and authenticated-user-id will be "*".
Likewise, the special-action-flags field mentions "compressed" and
"uncompressed" files; these flags specifically refer to the
compress
Unix program, which used the ".Z" file extension. This compression utility
has been superseded with e.g. gzip , bzip2 ,
and others these days. Thus the special-action-flags field in
ProFTPD-generated TransferLog entries is almost always "_".
SystemLog
If the site administrator wants to have proftpd log its messages
to a file rather than going through syslogd , the
SystemLog
configuration directive is the one to use. There is only one such file kept
for the entire daemon. See the
ServerLog
directive for keeping a similar log on a per-vhost basis. Note that the
DebugLevel
directive only applies to SystemLog files; it does not materially
affect the syslog-based logging messages.
ExtendedLog
The ExtendedLog
directive is used to create log files of a very flexible and configurable
format, and to have granular control over what is logged, and when. The format
of an ExtendedLog is described using the
LogFormat directive.
Multiple ExtendedLogs can be configured, each with a different
LogFormat .
Use of syslog versus file logging
Most sites will choose to have proftpd log via syslog (which is
the default) or to a file (via the SystemLog directive). In
either case, there is the question of logging verbosity, i.e.
which messages to log. This verbosity is determined by the
SyslogLevel
directive. ProFTPD will log everything by default, meaning that the default
SyslogLevel is effectively debug . If, however, you
have your proftpd configured to log via syslog, then you
should also check your /etc/syslog.conf file, to see what
additional filtering of log messages is being applied by syslog. For example,
if /etc/syslog.conf contained something like:
# Log anything (except mail) of level info or higher.
*.info;mail.none;authpriv.none;cron.none /var/log/messages
then ProFTPD's log messages below the info level would be filtered
out by syslog. When you are using syslog logging, the
SyslogLevel configuration directive applies only to the proftpd
logging, and does not control the additional syslog filtering.
For finer-grained control of the debug level log messages, ProFTPD
internally implements different levels for its debug log messages.
Currently ProFTPD has level 1 through level 10 debug messages.
The DebugLevel
directive is used control the verbosity/filtering of these messages. Since
these different debug levels are purely a ProFTPD convention, the
DebugLevel directive has no effect on syslog logging. Also, if
your SyslogLevel configuration uses a level higher than
debug , then the DebugLevel configuration will have
no effect — your debug level messages are already filtered
out by the SyslogLevel filtering.
The last point to mention is that the
SyslogFacility directive only applies to syslog logging; it has no effect on file logging.
Log Analysis
There are a variety of log analyzers available; these are just a few:
Log Rotation
On even a moderately busy server, the quantity of information stored in the log
files is very large. It will consequently be necessary to periodically rotate
the log files by moving or deleting the existing logs. This cannot be done
while the server is running, because the daemon will continue writing to the
old log file as long as it holds the file open. Instead, the server must be
restarted after the log files are moved or deleted
so that it will open new log files.
Another way to perform log rotation is using FIFOs as
discussed in the next section.
FIFOs (a.k.a. named pipes)
ProFTPD is capable of writing log files to FIFOs, from which another
process can read. Use of this capability dramatically increases the
flexibility of logging, without adding code to the main server. In order to
write logs to a pipe, simply create the FIFO at the desired path
(man mkfifo(1) ), and use that path in the logging configuration
directive.
One important use of piped logs is to allow log rotation without having to
restart the server. One such popular flexible log rotation program is
cronolog;
however, at present cronolog requires a small patch to enable it to read
from a FIFO (by default, cronolog reads data from stdin). Please contact
the author of this article for details concerning the patch.
Here's an example of FIFO-based logging script, based on one posted by Michael
Renner:
#!/usr/bin/perl
use strict;
use File::Basename qw(basename);
use Sys::Syslog qw(:DEFAULT setlogsock);
my $program = basename($0);
my $fifo = '/var/log/proftpd-log.fifo';
my $syslog_facility = 'daemon';
my $syslog_level = 'info';
open(FIFO, "< $fifo") or die "$program: unable to open $fifo: $!\n";
setlogsock 'unix';
openlog($program, 'pid', $syslog_facility);
syslog($syslog_level, $_) while (<FIFO>);
closelog();
close(FIFO);
exit 0;
More complex filtering can be added to such scripts.
If using FIFOs, there are some caveats to keep in mind. If you use in
init.d script to start standalone daemons, you can
add commands to start the FIFO logging programs first, before the daemon.
For inetd -run servers, consider wrapping up the necessary
commands for starting a FIFO reader and the server into a simple shell
script, or simply run the FIFO-reading program from an init.d
script, and save the overhead of starting that process, in addition to the
proftpd process, for each FTP session.
FIFO-based log readers are a very powerful tool, but they should not be
used where a simpler solution like off-line post-processing is available.
Note: In ProFTPD 1.3.3, the code was changed to use nonblocking
open(2) system calls when opening log files. This was done to
prevent a proftpd process from blocking indefinitely
(i.e. "hanging") if the log file was a FIFO, and there was no FIFO
reader process running when the log file was opened. However, some sites
do want this blocking open behavior, as their FIFO reader processes
may be temporarily busy. To get the pre-1.3.3 blocking behavior, you will
need to compile proftpd using the --disable-nonblocking-log-open
configure option.
SQL Logging
The mod_sql module also enables some powerful and complex
logging capabilities...
Trace Logging
ProFTPD also supports a much more verbose form of logging called "trace
logging". This form of logging is covered in greater detail
here.
Pid File
On startup, proftpd saves the process ID of the parent daemon
process to the file var/proftpd/proftpd.pid . This filename can be
changed with the PidFile directive. The process ID (aka PID) is for use by the administrator
in restarting and terminating the daemon by sending signals to the parent
process. For more information see the stopping and
starting page.
Scoreboard File
The last type of "logging" is done via the scoreboard file. The
scoreboard is binary-formatted file the server uses to store information
about each session; it is this file that is read by ftptop ,
ftpwho and ftpcount . The location for the
scoreboard file is determined by the
ScoreboardFile directive.
Frequently Asked Questions
Question: How can I direct the TransferLog
logging to syslog?
Answer: It is not currently possible to configure
proftpd to log TransferLog data to syslog. However, you
can configure an ExtendedLog which logs to syslog, and
which uses a LogFormat to log the data you wish. For example:
LogFormat xfer "%h %l %u %t\"%r\" %s %b"
ExtendedLog syslog:notice xfer
tells proftpd to log that LogFormat via syslog at the "notice"
syslog level.
Question: I have SystemLog in my
proftpd.conf , and when I use the SyslogLevel directive
to try to filter the messages which proftpd logs to my
SystemLog , it doesn't work. Why not?
Answer: When ProFTPD is configured to log everything
to a file via the SystemLog directive, it will do just that:
log everything, without any filtering, regardless of any
SyslogLevel directive. However, this changed in
ProFTPD 1.3.4rc1: in that release, the SyslogLevel directive was
made to apply to file-based logging as well.
Question: I configured my ExtendedLog
directive (or SystemLog , or other logs) to point to a FIFO.
The FIFO path exists. But when I try to start proftpd , it
fails to start with this error:
unable to open ExtendedLog '/path/to/extlog.fifo': No such device or address
Shouldn't this work?
Answer: The "No such device or address" error occurs
when you configure proftpd to log to a FIFO, and the
FIFO reader process has not yet been started. In times past,
proftpd would wait indefinitely on startup, waiting for the FIFO
reader process to start; now, proftpd tries to open the FIFO
in a nonblocking mode, so that it can fail immediately if there is no process
on the other end of the FIFO.
The "fix" is to make sure that any FIFO reader processes are started
before starting proftpd .
Question: How can I configure proftpd so
that nothing is logged for certain clients/IP addresses?
Answer: Using a combination of classes and the mod_ifsession module, this can be done using a configuration like this:
<Class invisible>
From 1.2.3.4
</Class>
<IfClass invisible>
# Disable all logging of these clients
SystemLog none
ExtendedLog /path/to/ext.log NONE
TransferLog none
</IfClass>
Question: How can I configure proftpd so
that it does no logging at all? I have a very small embedded system
for development/testing, and so do not need or want the logging.
Answer: To do this, you will need to disable much
of the builtin, default logging that proftpd does, e.g.:
# Discard the normal logging
SystemLog none
# Disable xferlog(5) logging
TransferLog none
# Disable logging to b/u/wtmp files
WtmpLog off
In addition, you may need to go through your proftpd.conf file
(as well as any Include config files), and remove all
ExtendedLog and TraceLog directives. Also remove
any per-module *Log directives like BanLog ,
SFTPLog , SQLLogFile , TLSLog , etc.
You might be tempted to symlink the log files configured to
/dev/null , rather than changing the proftpd.conf .
This approach can work, if you also use the AllowLogSymlinks directive, i.e.:
# Allow proftpd to write logs to symlinks; note that this is insecure,
# as the symlinks might be changed to point to other files such that
# proftpd will overwrite them.
AllowLogSymlinks on
Question: I see:
wtmp /var/log/wtmp: No such file or directory
in my logs. What is WtmpLog logging? The description in the
documentation is quite vague.
Answer: The wtmp logging support is
not specific to proftpd , and instead is a more general Unix
facility; this is why the ProFTPD documentation does not cover it in great
detail. To learn more about wtmp (or any of its other
incarnations: wtmpx , utmp , utmpx ),
please find their related man pages.
Now to make the "No such file or directory" log message go away, simply tell
proftpd to stop trying to use wtmp logging by using
the WtmpLog
directive:
WtmpLog off
in your proftpd.conf .
Question: I usually run in a non-English locale; my
ProFTPD version is older than 1.3.6, and I use fail2ban .
Unfortunately, fail2ban has trouble with the non-English
localized dates in the syslog messages, e.g.:
juil. 28 16:42:17 server-hostname proftpd[9423] server-hostname ...
in my logs. How can I get ProFTPD to log using the English locale, for
working with fail2ban properly?
Answer: The locale-related environment variable which
governs how dates are formatted is the LC_TIME environment
variable. Thus you need to set that environment variable, before
ProFTPD is started, to use the English locale if you want English localization,
e.g.:
$ export LC_TIME=en_US.UTF-8
$ service proftpd start
Note that the above is only really needed due to the older version of ProFTPD.
In later version of ProFTPD, the syslog logging format changed (to avoid such
localization issues), so that it now looks like:
2017-07-28 16:42:17 server-hostname proftpd[9423] server-hostname ...
This should help many such log-parsing issues.
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