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How to setup a Linux firewall

Introduction

If you setup a Linux box, you want to setup a firewall before you connect your computer to the Internet. If you are setting up a remote server, it should only have the SSH port open. Connect to it, setup the fire, then only install the other servers and open ports as required (and only ports that need to be connected from the outside.)

Any port that you open without the firewall already setup is at risk. You may want to install PHP and along will come a database which may open a port to the Internet. Something that you just don't want to happen.

Setup Firewall

To ...

Adding a group for to a logged in Linux user

Once in a while I want to add my user to a group and then right away make use of that group.

Unfortunately, in general Unix kind of forces you to re-log in for the new group to be attached to your account.

However, a command has been added, a while back, to do just that on the fly. Not something you would want to use in a script, but at least, it works for me when doing a few things here and there.

In my case, I wanted to run QEMU, which I hadn't done in a while, and the system told me that it could not open the KVM, the error: kvm permission denied.

The problem was that I was not part ...

Sep 27 00:58:42 halk postfix/error[16751]: 628254C02F0: to=<mo_fax@m2osw.com>, relay=none, delay=1.8, delays=0.06/1.6/0/0.14, dsn=4.4.1, status=deferred (delivery temporarily suspended: connect to mail.m2osw.com[69.55.231.156]:25: Connection timed out)

My syslog was filled up with errors such as this one:

    Sep 27 00:58:42 halk postfix/error[16751]: 628254C02F0: to=<mo_fax@m2osw.com>,
    relay=none, delay=1.8, delays=0.06/1.6/0/0.14, dsn=4.4.1, status=deferred
    (delivery temporarily suspended: connect to mail.m2osw.com[69.55.231.156]:25:
    Connection timed out)

I've been wordering for a while, since I can use Thunderbird with a direct connection to my server, I was not too concerned, but tonight I really needed to support those emails because I have work to do that requires it.

Got NVG510 to setup?
Hacking my ...

Your Bookmarks are auto-backed up in SeaMonkey! (and maybe FireFox?)

I started the stock SeaMonkey browser by mistake as my Unity icons disappeared (i.e. seamonkey as is on my command line started /usr/bin/seamonkey which is not the correct version!) This had several bad side effects. For of all, it destroyed my bookmarks (argh!) and then it decided to install the 64bit Flash plugin. That did not work well since the version I like is a 32bit version.

Once I had the correct version started again, each time it was trying to open a Flash animation, it would be "stuck" for a few minutes, until I tried to open a page with a movie in a Flash shell. That ...

Check whether a form is open in MS-Access

MS-Access has forms, but no real means to know whether a form exists. It looks like you could go through the list of forms (Forms.item(i)) but I'm not too sure that would work in all circumstances.

Instead, I used code I found on another site which runs a system command to determine whether a form is currently attached to a window (has a state other than zero.)

The code looks like this:

IsLoaded = False
If SysCmd(acSysCmdGetObjectState, acForm, strFormName) <> 0 Then
    If Forms(strFormName).CurrentView <> 0 Then
        IsLoaded = True
    End If
End If

The first ...

Binary (Hexa) File Editor for Windows

Got an email from SourceForge.net today and they mentioned a new binary editor that works under MS-Windows.

Yes, they have one in DevStudio, but it's cumbersome to open a file in that more. You have to go through hoops and it often changes a tiny bit between versions and even just installs!

This one's small and fast and works on large files too.

It's called Frhed.

Linux Firewall "missing" igmp protocol... Watch out on reboot!

I just updated Linux to the newest version for Ubuntu 10.04 and got an error with the firewall...

 * Setting up the firewall iptables...
iptables-restore v1.4.4: Couldn't load match `igmp':/lib/xtables/libipt_igmp.so: ... 
                             ... cannot open shared object file: No such file or directory

The fact is that the iptables code is now using a set of .so files to handle each protocol and it is found in the /lib/xtables folder. And there is no libipt_igmp.so file in there... so you cannot change anything against such packets. That's it...

I tried to use 2 as the

Windows 2000 SP4, new logon policy forced to Roaming by default.

Not too long ago, I accepted the update from Microsoft to go to MS-Windows 2000 SP4. Neat. Except that when I rebooted (I think the 2nd time, but not totally sure, my wife used the computer in between, it seems...) it could not load my profile anymore.

List Open Files

This is a quick note so I can find the command I need to use to list open files.

My search will work this time.

lsof stands exactly for "LiSt Open Files"

That gives you a list of all the files opened by your system, process by process. It can be useful to know if you are developing a program or if you are limited in the number of files opened at once.

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