Mon, Aug 30, 2004 8:38 pm
Blosxom Calendar Plugin
A plugin to add a calendar to a
Blosxom blog is available from
Mt. Molelog or from
When I first installed the plugin, I received an "Error 500" error from
my blog's webpage with the error message "Premature
end of script headers: blosxom.cgi". The webpage loaded correctly once
I changed the ownership of the state directory, which lies
beneath the plugins directory. I used the following commands
to change the user and group for the directory:
chown apache state
chgrp apache state
I used apache as the owner and group, since my web server runs Apache
webserver software. I could also have used
chmod 777 to
make the directory world writable, but that would be much less secure,
since anyone else on the system could then have write access to the
Mon, Aug 30, 2004 5:36 pm
No PTR Record
If you receive bounced messages with "cannot resolve PTR record"
or "(reason: 554 5.7.1 The server sending your mail [xxx.xxx.xxx.xxx] does not
have a reverse DNS entry. Connection Rejected" as
the reason listed for the message bouncing, with "xxx.xxx.xxx.xxx"
representing the IP address for your SMTP server, or see messages,
such as "Relaying temporarily denied. Cannot resolve PTR record for"
followed by your mail server's IP address
in your /var/log/maillog file, then the email server
that received the message checked the Internet Protocol (IP) address
for the sending server. It then tried to do a "reverse lookup"
on the IP address to obtain the name of the server. If it couldn't
perform the reverse lookup, then it would bounce the message
with a statement that it couln't resolve the PTR record. A PTR
record is an entry in a Domain Name System (DNS) server that
maps IP addresses back to names.
If you see references to
http://postmaster.info.aol.com/errors/421dnsnr.html for messages
destined for aol.com or netscape.net users, it is due to the same
issue. Netscape.net is owned by
An email server adminsitrator may configure an email server to
perform such a check to block spammers. I suppose the thinking
is that systems used by spammers are more likely not to have
PTR records in a DNS server. But, since many email
servers not used by spammers will also not have PTR records, I
believe such a check is likely to block as much, if not more,
legitimate email than spam. And it is hardly an effective means of
eliminating spam, since many systems transmitting spam will
have PTR records.
A small business may have its own email server with a domain name
that maps to an IP address, but the company's ISP may not have an
entry in a DNS server that maps that IP address to a name. In such
a case, the business may find that email to some domains bounces
with the error message about the missing PTR record.
If you are a system administrator with users reporting that they
are receiving bounced messages with the "cannot resolve PTR record"
for messages addressed to certain domains, then you can configure
your email server to send email to just those domains through
another email server instead. For instance, your ISP may have
restrictions that prevent you from sending email to more than a
limited number of recipients at one time. You may have a mailing
list that has more email addresses than the ISP allows to be
reachable with one message. So you need to use your own email
server to reach all of the members of the mailing list. But
some of the mailing list members may be using email servers
that attempt to look up a name from the IP address of the sending
server contacting them.
If you are running sendmail to transmit email, you can edit
mailertable, which will be in /etc/mail on a RedHat Linux system.
The mailertable file contains special treatment information for
a specific domain or family of domains.
As an example, suppose email to firstname.lastname@example.org is
bouncing with the message about "cannot resolve PTR record".
You can add the following line to /etc/mail/mailertable:
Once you've added the line, you need to run makemap, to produce
the mailertable database sendmail uses. You then need to restart
makemap hash /etc/mail/mailertable </etc/mail/mailertable
The first command above will produce or update the file
I am presuming that you already have mailertable support within sendmail.
You can check if that is the case by looking for mailertable within
your sendmail.mc file as below:
grep mailertable /etc/mail/sendmail.mc
You should see something like the following, if sendmail is already
configured for mailertable support.
FEATURE(`mailertable',`hash -o /etc/mail/mailertable.db')dnl
The above example presumes that the ISP server, smtp.centrivity.net,
does not require authentication. If the server requires authentication,
then you will need to modify the access file, which you may find
in /etc/mail. Let's say that the smtp.centrivity server accepts
plaintext authentication with a userid of jsmith and a password of
GrassHopper. You could enter the following line in /etc/mail/access
to have sendmail on your system send the necessary authentication
information to the smtp.centrivity.net server.
AuthInfo:smtp.centrivity.net "U:jsmith" "P:GrassHopper" "M:PLAIN"
You would then also need to produce or update /etc/mail/access.db
using the makemap command.
makemap hash /etc/mail/access </etc/mail/access
In the case of the ISP's server requiring authentication in order
to send email through it to a destination address that is not an
email addres on the ISP's servers, you would edit the mailertable
and access files before restarting sendmail with
- Using 'mailertable' in
SBC-Yahoo ® Authenticated SMTP
Sat, Aug 28, 2004 12:32 am
Determining the Country Associated with an IP Address
You can use GeoIP to look up the country associated with a given IP
address (you can also give it a hostname to determine the country).
To create the GeoIP program geoiplookup, you can download the
C source code from
You will need a C compiler to compile the code. If you intend to use it on a
Linux or Unix system, you will have a C compiler on the system, so just
follow the instructions below to create the geoiplookup program or read the
INSTALL file that comes with the file you download from the MaxMind website.
If you intend to install it on a Windows system, read the READMEwin32.txt
file that is in the .gz file you download.
Unzip the downloaded file, extract the contents of the resultant
tar file and then change the working directory to the GeoIP directory
created from the contents of the tar file.
tar -xvf GeoIP-1.3.6.tar
Then run the
(installation instructions are in the INSTALL file created in the GeoIP
directory, but are also summarized here).
You can then issue the command
make check to run self-tests of
the package, but this step isn't required. You should then type
make install to install the software.
At this point you won't need the program binaries and other files in
the source code directory and they can be removed with
clean. You can also remove the files created by
by issuing the command
make distclean. You can also remove the
GeoIP directory and its contents, if you wish, since
installs the package's files in /usr/local/bin, /usr/local/man, etc.
rm -fr GeoIP-1.3.6
When the program is installed, you will have a geoiplookup program in
/usr/local/bin. You can use that program to lookup the country associated
with an IP address or hostname. The country is based on the registration
for the IP address, i.e. particular blocks of IP addresses will be associated
with particular countries or at least areas of the world. The company
using the IP address may be based in some other country, however. For
GeoIP Country Edition: US, United States
The company has their website, eapplique.com, hosted on a server with
a US IP address. But if you issue the command
eapplique.com, you will see the domain
name is registered to a company in India (the company provides website
design services). So geoiplookup gives you an indication of where a
server is likely to be located, but not necessarily the location of a
particular company using that server. Companies and individuals may
use servers located in other countries.
THE SCS GROUP (EAPPLIQUE-DOM)
K 3/17, DLF Phase II
GURGAON, HARYANA 122002
Domain Name: EAPPLIQUE.COM
For an example of a lookup for an IP address, here is another example:
GeoIP Country Edition: HK, Hong Kong
Tue, Aug 24, 2004 11:10 pm
Changing the "From" Address in Outlook 2000
To change the "From" address of a message in Outlook, create a new
account using the address you wish to use as an alternative "From"
address. You can create a new account by the following steps:
- Click on Tools.
- Click on Accounts.
- Click on the Mail tab at the top of the window.
- Click on the Add button then select Mail
- Put in the display name you wish to appear in the message.
This is just whatever you wish to be the name recipients will
see with the email address, e.g. "John Smith".
- Click on the Next button.
- Type in the alternative e-mail address you wish to use.
- Click on the Next button.
- Select whether the server you wish to use is a POP3 or IMAP server
and specify the server names for incoming and outgoing email.
- Click on the Next button.
- Put in the password if you want the system to remember it rather
than prompting you each time, otherwise leave it blank and uncheck
- Click on the Next button.
- Select your connection method and click on Next.
- Click on the Finish button.
If this isn't an email account you will be checking regularly, but
just an alias, i.e. an alternative address that points to the same
account as one you are already checking, select the account by clicking
on it and then click on Properties. Then uncheck "Include this
account when receiving mail or synchronizing". Then click on Ok.
Then click on Close to close the Internet Accounts
window. You might want to send a message with email@example.com
as the "From" address, rather than firstname.lastname@example.org, so in the case
that email@example.com is just an alias pointing to the
firstname.lastname@example.org mailbox, you would uncheck the "Include this
account when receiving mail or synchronizing", since it isn't a
Once you've gone through the above procedure, you won't need to repeat
it again and can use the alternate address you specified as the "From"
address in messages by the following procedure:
- Compose a message in Outlook the way you normally would.
- You may see "To", "Cc", and "Subject" fields, but no "From"
field. Click on the Options button.
- Click on the downward pointing triangle to the right of
the Send message using field to see the list of email
addresses you can use in the "From" field. Pick the one you
wish to use and then click on the Close button.
- Fill in the "To" and "Subject" fields as usual, edit the
message and then click on the Send button. The message
will now go out with the address you picked for the "From"
Mon, Aug 23, 2004 11:05 pm
Keeping a Linux System's Time Accurate
PC and workstation clocks are not highly accurate and will tend to drift
from the correct time over time. To keep the system's clock accurate, one
can use the Network Time Protocol (NTP). The fact that a system's clock
is off by a few minutes may not seem important at first, but if you have
to troubleshoot problems involving multiple systems, you will realize that
it can take much longer to troubleshoot if the clocks on the systems
vary and you must mentally adjust the times to determine the order
NTP software will provide the capability for a system to contact a
time server, which provides an accurate time source. In the United
States time servers may be tied back to the time source provided
by the National Institutes of Standards
and Technololgy (NIST).
On RedHat Linux systems, you can
use the ntp package to set up your system to obtain time from a time
server using NTP.
Installing and configuring the ntp package on RedHat Linux is detailed below.
The example below uses
ntp-4.0.99k-15.i386.rpm, which is version 4.0.99k release 15 of the ntp
client. If you are using a later version of RedHat Linux, a newer version of
ntp may be available for your version of Linux. Except for the RPM file name,
the installation and configuration process should be similar.
Install the package, e.g.
rpm --install ntp-4.0.99k-15.i386.rpm.
Edit /etc/ntp.conf file. Add a server line to point to
a publicly accessible time server, e.g.
server 184.108.40.206 to
use the time server lennier.cc.vt.edu. You then should have
lines similar to the following in the ntp.conf file:
server 127.127.1.0 # local clock
fudge 127.127.1.0 stratum 10
Use chkconfig to configure the service to start when the sysem boots
chkconfig ntpd on
Start the service.
If you wish to immediately update the time to match that on the time server,
you can use the ntpdate command, e.g.
ntpdate -b lennier.cc.vt.edu
You can check that the service is functioning with the ntpq command.
remote refid st t when poll reach delay offset jitter
lennier.cc.vt.e Tick.UH.EDU 2 u 34 64 1 28.516 0.340 0.000
LOCAL(0) LOCAL(0) 10 l 9 64 1 0.000 0.000 0.000
You can check to see whether your system is functioning as an NTP server,
which means it will be listening on NTP UDP port 123 by using the netstat
netstat -a | grep "ntp"
udp 0 0 gna.somewhere.com:ntp *:*
udp 0 0 localhost.localdoma:ntp *:*
udp 0 0 *:ntp *:*
You should see the system name followed by ":ntp", which indicates it
is listening for connections on the NTP port, UDP port 123.
If you are blocking access to the system with a firewall, you will
need to provide a rule for UDP connections to port 123, if you want to
allow other systems the capability of obtaining the time from your
If you wish to trace the path back through a sequence of time servers
to find the master time source, you can use the ntptrace command.
localhost.localdomain: stratum 3, offset 0.000100, synch distance 0.22896
lennier.cc.vt.edu: stratum 2, offset -0.016537, synch distance 0.04396
time-b.nist.gov: stratum 1, offset -0.012730, synch distance 0.00000, refid 'ACTS'
The example above shows that the system gets its time from lenier.cc.vt.edu,
a stratum 2 server, which in turn gets the time from time-b.nist.gov, a
stratum 1 server.
Decibels Linux NTP Tutorial
NIST Internet Time Service
NTP - The Network
ntpq - standard NTP query program
ntptrace - trace a chain of NTP servers back to the primary source
US Naval Observatory
NTP Network Time Servers
Using the Network
Time Protocol to Sync Your Network
Keeping Time on Windows
Wed, Aug 11, 2004 12:07 pm
Determining the Version of Irix Running on an SGI System
To determine which version of the Irix operating system i(OS) you are running
on a Silicon Graphics, Inc. (SGI) system,
use the "uname -R" command.
The second of the two values, minus the trailing character, is the actual
version number, e.g. 6.5.19 above. SGI calls this value the "extended" version
The "-R" option to the uname command is unique to Irix systems.
See the Irix
uname manpage for further information on version numbering and options
for the uname command on Irix systems.
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