Edit:
Someone made a comment, as people on the internet are prone to do, so here’s the long-form non-one-liner version:


#!/usr/bin/perl
my $addDays = shift;
my ($second, $minute, $hour, $day, $month, $year, $dayOfWeek, $dayOfYear, $daylightSavings) = localtime(time());
my ($fsecond, $fminute, $fhour, $fday, $fmonth, $fyear, $fdayOfWeek, $fdayOfYear, $fdaylightSavings) = localtime(time() + $addDays*24*60*60);

print "today is: $month/$day/$year\n";
print "$addDays days from today is: $fmonth/$fday/$fyear\n";


Run it as:

rob@laptop:~$ fdate.pl 50
today is: 1/25/2012
50 days from today is: 3/15/2012


So I wrote a little script, and put it in /etc/network/if-up.d/ named “jumbo-frames.sh”. The if-*.d/ structure is designed for exactly this purpose: run a script when an interface comes up. The basic premise is: If I’m plugged into a wired network (eth0) in the lab (domain or IP address match certain parameters), then set the MTU to 9000 (jumbo frame support), otherwise assume the network has a normal MTU (1500). This allows the system to reconfigure on the fly if I put it to sleep and go visit a customer.

Here’s the code:

#!/bin/sh
# Set support for jumbo frames when at home on wired network, else do not.
# Determine home network based on IP address and DNS-determined name.
# $IFACE should be set by the caller.

if [ "$DOM" = "$HOMED" ]; then
$IFC $IFACE mtu $MTU
elif [ "$NET" = "$HOMEN" ]; then
$IFC $IFACE mtu $MTU
else
$IFC $IFACE mtu $DEFMTU
fi


First step is to determine which servers are responsible for mail delivery inbound for the domain you’re sending to. You do this by looking in DNS for the “MX” type records. These are provided in the format “priority servername.domain.” Priority is reverse-ordered. The easiest way to remember priority order is that it’s the order in which servers are attempted.

rob@rob-kubuntu3:~$ dig MX totalnetsolutions.net +short
10 docsmooth.isa-geek.net.
rob@rob-kubuntu3:~$ dig MX likewise.com +short
10 server1.inboundmx.com.
20 server2.inboundmx.com.

This tells you the servers, in order, that *all* mail will be sent to for the domain listed. So, anything to my likewise.com address will go to server1.inboundmx.com. The higher priorities are only used if the lower priorities fail to answer. If no server answers, the mail is held by the sender and retried, generally every 1 or 4 hours for up to 4 days, but this retry is configured on the *sending* server. That means, your own email admin (or you, if you’re the mail admin).

Next thing to check is: does the server work, and is it your sender, or their receiver? Check with telnet!
Stuff I type is in red:

rob@rob-kubuntu3:~$ telnet docsmooth.isa-geek.net 25
Trying 99.29.179.119...
Connected to docsmooth.isa-geek.net.
Escape character is '^]'.
220 totalnetsolutions.net Microsoft ESMTP MAIL Service, Version: 6.0.3790.4675 ready at Tue, 31 May 2011 08:43:08 -0500
HELO
250 totalnetsolutions.net Hello [12.130.116.175]
MAIL FROM: me@me.com
250 2.1.0 me@me.com....Sender OK
RCPT TO:you@you.net
250 2.1.5 you@you.net
DATA
354 Start mail input; end with .
from:me@me.com
to:you@you.net
subject:test manually
test
test
.
250 2.6.0 Queued mail for delivery
quit
221 2.0.0 totalnetsolutions.net Service closing transmission channel
Connection closed by foreign host.

The last “.” is SUPER important – it tells the mail server when you’re done sending that email. You could use that channel to send other messages, rather than sending “QUIT” if you’d like. You might notice that I entered the “From” and “To” lines twice. The first entries are for the SMTP header (analogy would be the message envelope), and the second entries are for the MIME headings (analogy would be the return address header in a formal postal letter, if anyone sends those). The MIME headings are what most mail programs display, and actually don’t technically need to match the SMTP header (but if MIME and SMTP don’t match many anti-spam programs will throw out the message).

The MIME header is pretty complex, but not order-dependant, although I prefer to enter it in order, so that I can be sure I don’t miss anything.
If you want to add an attachment, just base64 encode it first with:
perl -e 'use MIME::Base64; qw(encode_base64); print encode_base64("@ARGV");' cat attachment-to-send.zip
Then you can just paste it into the email. In the MIME heading (right after the subject), just add (with the appropriate mime coding, probably application/octet-string:

------=_NextPart_000_000D_01CC1C41.21F38080
Content-Type: application/zip;
name="attachment-to-send.zip"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
filename="attachment-to-send.zip"
<paste your base64 encoded attachment/ >
Content-Type: multipart/mixed;
boundary="----=_NextPart_000_000D_01CC1C41.21F38080"
------=_NextPart_000_000D_01CC1C41.21F38080
Content-Type: text/plain;
charset="us-ascii"
Content-Transfer-Encoding: 7bit

Now that you know *how* to send an email message by hand, you can use the returned error codes to troubleshoot where the message may be disappearing. Remember, that this just gives you transport troubleshooting between yourself and the initial destination mail server. Many large (and even medium-sized) organizations will have a perimeter mail server which then forwards the message to one or more internal servers. If the mail is being dropped at that point, you’ll have to contact the reciever with the proof that their server is accepting your messages.

On a Samba server joined to AD with winbind, this is easy to deal with because Samba’s winbind can treat the computer accounts just like user accounts, and assign them access to the unix filesystem with whatever backend has been configured. When a Samba server is joined with Likewise, however, the machine accounts are not visible, and the “username is invalid” message comes up.

Fortunately, Samba gives us a method to handle this, in form of the “username map” directive in /etc/samba/smb.conf.  There are two ways to use this, the first is with the username map file.
In smb.conf, to simply add:
[global ]
username map = /etc/samba/smbusers
then create a file named /etc/samba/smbusers and populate it with localuser=aduser pairs, like:
COMPUTER1$ = compacct
COMPUTER2$ = compacct
CITRIXFARM1$ = citrxact
and so on. Lastly, you’ll have to add the local accounts from the pairs above:
useradd -c "Account for AD Computers to use Samba" compacct -G users -u 998
useradd -c "Account for AD Citrix Servers to use Samba" citrxact -G users -u 999
Then, whenever one of the AD computers in the list attempts to access the Samba share, it’ll be mapped to the local account.

The problem with this is when you have a lot of servers, like a Citrix MetaFrame farm, or a Windows Server 2008 R2 Remote Desktop Services farm, that may be changing frequently, because managing that file could get hard. In this case there is the username map script directive, which is added to smb.conf as:
[global ]
username map script = /usr/lib/samba/auth/machine-acct-map.pl
Then download this script and save it in /usr/lib/samba/auth/ and make it executable (chmod +x /usr/lib/samba/auth/machine-acct-map.pl). Then run:
useradd -c "Account for AD Computers to use Samba" compacct -G users -u 998
Now, all computers which access the share will be remapped to the “compacct” user, and you won’t have to manage a file for every time the server farm changes.

Get the file here.

Apperantly Solaris 10 and OpenSolaris have a little quirk around how they work with DHCP and setting the system’s DNS name. In our test lab, all our systems are assigned addresses via Microsoft DHCP, which then registers (and un-registers) non-Windows systems in DNS properly. However, the x86 Solaris systems we built for a customer test came up with name “unknown”, every single reboot. Changing /etc/hosts and /etc/hostname.pcn0 or /etc/hostname.vmxnet0 (physical or VMWare) to reflect the new proper hostname, however, didn’t affect the server on reboot – the settings would still be there, but not reflected in the OS, in /etc/hosts, or in DNS.

A bit of searching turns out a bunch of posts talking about editing /etc/nodename to put in the system name, but that file doesn’t exist out of the box on a “complete” or “minimal” install, and I’m always hesitant to create new files by hand in /etc/ unless I’m 100% sure that’s what’s needed. According to this post on Sun.com, some logic, and some testing, I think what’s going on is:

1. Solaris expects DHCP to set the hostname of a system based on MAC address
2. In case DHCP does not set a hostname via MAC address, or if that hostname is wrong, Solaris provides an override mechanism called /etc/nodename
3. Because it’s an override, /etc/nodename is not created as a blank file, since that could be construed as “override DHCP with nothing”
4. Therefore, every new box I build needs touching after final login

I’m not a huge fan of this, but I’m also not a fan of the number of times I need to click a mouse on an OS Install using software from the last year. The short version of all this is:

If you have a Solaris 10 box on DHCP named “unknown”, best practices is to set the hostname on the DHCP server. Otherwise echo newservername > tee /etc/nodename and reboot. (with “tee” in the pipeline, you can “sudo” this command as well).

With my recent upgrade of that same laptop to Kubuntu Gutsy Gibbon, I kept the laptop-mode.conf file a bit closer to the maintaner�s version. There are some changes to the �dirty-writeback-centiseconds� and the �dirty-background-ratio� values from what I posted, and my issue seems to have gone away. I�ve been able to go back to running my Windows 2003 SBS server with a Centrify DirectControl lab environment and a RHEL 4 Oracle 10g server attached at the same time.

The configuration files that work MUCH better are attached here:

laptop-mode.conf

cpufreqd.conf

1. Same as before: why are you changing IPs? In larger environments, I do this because of a physical move of just one site. If the networking team doesn�t have the new subnet up and routing, don�t start!
2. Make sure the new site (if required) is set up in AD. If I�m moving DCs from one physical location to another, I will build a new site, rather than re-using the old one, because the new site often has better connectivity, so the site link costs are changing.
3. Add the new IP to the DC you�re moving (DC01 for this). Same as before: don�t remove the old one, just add the new.
4. On DC01, do the following to verify registration worked:
   ipconfig /registerdns
   Wait a few minutes.
   nslookup
server DC01
set type=A
DC01.foobar.local
foobar.local
server DC02
DC01.foobar.local
foobar.local
   The answers from DC01 and DC02 should be the same, with possibly different orders. The important thing is that the new IP address and the old IP address show up for both queries on both servers.
5. Shut down DC01, pack it up and move it. (Or just plug it into the new network.)
6. Boot up, verify that DC01 has network connectivity, and that other systems can see that it has the new IP.
7. If you haven�t, make the new IP primary (change order in Network settings), make sure the DNS and WINS servers are correct and reachable (Remember that Windows 2003 DNS should point to itself).
8. Once verifying that AD is replicating across sites properly (up to 15 minutes in my experience), remove the old IP, ipconfig /registerdns, and reboot.
9. When it comes back up re-verify that AD is still replicating, and you should be set.

I would point out that when doing a change this big to your environment, reviewing your AD replication, DNS forwarding, and WINS topology is a good idea.

However, because I mostly design Windows networks, I also run VMWare Workstation 6 with the following VMs: Windows XP Pro joined to primary domain (full workstation with Office 2003, Visio, Outlook (and EMC EmailExtender plugins), Windows Admin Pack, Resource Kit, SQL Enterprise Manager, and Exchange Admin Pack), Windows Vista Enterprise, Windows 2003 DC, Exchange, SQL server, Windows XP Pro joined to VM domain, RHEL 4, RHEL 5, and a Live-CD system that I often use to test bootable CDs. And a sysprep�d Windows install.

All that, plus Evolution caching my email and Firefox being disk-happy (did you ever �strace -p $(pgrep firefox) -e trace=open,close,read,write�? It�s busier than Evolution during an offline mail check!), means my 7200 RPM 160GB SATA disk gets hammered. Me also using laptop-mode-tools changing my vm.dirty_writeback_* settings and read/write cache isn�t helping either, I�m sure.

Today and yesterday I ran into an issue where my disk would begin a sync that would last 10-20 minutes, leaving me unable to work the entire time that was happening. Hunting down WHAT was causing this, however, was even more frusterating than it happening (If I shut down any of the 3 above-mentioned programs, the problem went away – it only happened with all 3 open). In Windows, you can open Task Manager, go to the �Process� tab, click �View-> Columns� and add �IO Write Bytes� and �IO Read Bytes� and watch the numbers count up. Or you can use Perfmon and look at IO reads/writes/bytes per second or total, and know immediately what�s causing all your disk IO pain. I still don�t know how to do this in Linux.

First, any hunt for �disk utilization� and �Linux� on Google directs you to hundreds of sites, forums, and blogs evangelizing the wonders of �df� for disk utilization. Yes, it�s really nice to know how much free space I have on my hard drives- that�s why I have SuperKaramba to tell me. But when a problem hits and leaves me unable to work, it�s useless.

�iostat -k 1? is great – you�ll know immediately which disk is being used, and how hard. But on a laptop with a single disk, you already know.

�top� sorted by process-state will show you what�s in �waiting on IO� state, but not what�s CAUSING the IO that�s causing everything else to wait.

�sar� seems to be the only tool that can provide per-process IO stats, but it has to be pre-set up to write to a log. And I can�t begin to guess how well that will work when my disk is at 100% utilization (peaked at 120tps today).

So if anyone knows of any way to know what�s causing disk IO in a �right now� fashion, please comment or email me. And if you�re curious more about my problem:

1. Only happens when VMWare (with a guest), firefox, and Evolution are all running.
2. VMWare with multiple guests runs fine, and never has this issue.
3. rauch@lt00-bofh:~$ free
total used free shared buffers cached
Mem: 3348960 1099216 2249744 0 68668 533124
-/+ buffers/cache: 497424 2851536
Swap: 6000268 0 6000268
4. Happens with Laptop_mode disabled or enabled, on AC or on battery
5. �sync� causes the exact same symptoms, leading me to believe that somehow I�m getting a LOT more dirty pages than my parameters are set at.
6. dirty_background_ratio
1
dirty_expire_centisecs
60003
dirty_ratio
60
dirty_writeback_centisecs
60003
7. For now, I just close Firefox when I have VMWare open, which means I spend a lot more time in IE than I want to.

As a final note, I�ve updated my Linux EVDO post here with my new built-in card�s info.

For all 3 of them, the only difference was the modprobe line, for vendor and product ID, as noted below.
Merlin S620:
modprobe usbserial vendor=0x1410 product=0x1110
Sierra 575:
modprobe usbserial vendor=0x1199 product=0x0019
Dell Sprint 5720 PCI-Express Modem
modprobe usbserial vendor=0x413c product=0x8134

I saved the appropriate PPP files at /etc/ppp/peers/1xevdo and at /etc/chatscripts/1xevdo_chat. In this post, I�ve blanked out the parts that are particular to my install (phone number), but it should be pretty easy to recreate your settings.

/etc/ppp/peers/1xevdo:

-detach
ttyUSB0
115200
debug
noauth
defaultroute
usepeerdns
user $(full-phone-number)@sprintpcs.com
show-password
crtscts
lock
lcp-echo-failure 4
lcp-echo-interval 65535
connect '/usr/sbin/chat -v -t3 -f /etc/chatscripts/1xevdo_chat'

/etc/chatscripts/1xevdo_chat:

'' 'AT'
'OK' 'ATZ'
'OK' 'ATE0V1&F&D2&C1&C2S0=0'
'OK' 'ATE0V1'
'OK' 'ATS7=60'
'OK' 'ATDT#777'
CONNECT CLIENT


Since I do several bits of work through the console, including accessing my Cisco VPN, and in some cases naim and tmsnc (console AOL and MSN chat) inside a screen session, scripts for these setups work great for me. I wrapped the whole thing up inside a bash script called $HOME/bin/evdo.sh – and I just call that when I want to get online, after inserting the card.
~/bin/evdo.sh:

sudo /sbin/modprobe usbserial vendor=0x1199 product=0x0019
sleep 5
sudo /usr/sbin/pppd call 1xevdo


The sleep statement helps make sure that the modprobe has completed, scanned the device, and settled before calling PPP.

My Dell D620 arrived, and I was able to quickly determine the changes for an �always there� card, vs. a pluggable PCMCIA card.
First I created /etc/modprobe.d/usbserial with the line:
options usbserial vendor=0x413c product=0x8134
and added �usbserial� to the end of /etc/modules so that the card would always come up at boot (sudo lspci -v | less to find the exact product ID and vendor – I only have 2 �Dell� devices on my laptop). I set my radio kill switch to affect only my EVDO and bluetooth radios, letting the software (~/bin/rfkill.sh in Linux and the Dell software in Windows) handle the WiFi – I use WiFi all the time, but only want the battery-draining EVDO in a few specific instances. So I added �cat 0 > /sys/bus/pci/devices/0000\:03\:00.0\rf_kill� to my �evdo.sh� file to kill the wireless when I wanted to use EVDO – no need to ever have them both on.