Category Archives: nix

Proftpd: listen on single ip

nix, , ,

I don't use ftp, I always use sftp/scp/rsync over ssh or even a fuse remote filesystem for transferring files but wordpress 2.5 comes with this nice feature to upgrade plugins automatically from the web admin interface that needs ftp.

the problem is I don't want to enable the ftp service and make it available to the rest of the world just for that.

So what are my options?

  1. I know I could just add a firewall rule and just not allow anyone else except for localhost to connect
  2. set proftpd to listent only on localhost ( 127.0.0.1)

The #1 depends on what firewall you have so I'm not going to discuss it here. You also may not want to do that because of some other reasons you might have.

#2 needs the following two options in proftpd.conf:

DefaultAddress 127.0.0.1
SocketBindTight                 on

Now restart proftpd and you're done.

Explicitly ignorant in Unix

nix, , , , , , ,

I'm working on a patch for antinat, to make it do some cool/weird stuff that it can't do at the moment.

In case you're wondering antinat is a great implementation of a socks server. It supports socks4, socks5 with user/password authentication, accept/reject acls based on user or ip, easy configuration in an XML file and it's also multithreaded ( ok maybe this is not so great for some but I like it ).

I'm not going to write about the patch I'm working on but maybe I'll write about that in another post.

While I was looking over it's source code I found this funny comment right before a function that was used to handle the SIGPIPE signal:

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This is funny but the comment has a good point. If you write an application and it tries to write to a connection that was closed, your program will receive a signal with the code SIGPIPE, which means ( according to the man page of the kill program) that if the proces does not have a default handler for SIGPIPE then it will just exit. So there you have a big problem.

The simple solution is to just set your own signal handler for SIGPIPE . So you have to set a function that will be called when the program receives a SIGPIPE and your function doesn't really have to do anything about it, so it will just ignore it and reset the handler to itself.

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But if you don't explicitly set this, your process will just die upon receiving a SIGPIPE and you really don't want that especially when writing server applications.

How to make linux feel like windows

nix, , , ,

Anyone missing windows ? Not me, but sometimes is good to go back to windows just to see how it was in the old days when nothing worked well and you would have a crash every few minutes or reinstall once a week.

Do that and you'll realize how privileged you are for using a Unix like os and be thankful to those that develop and contribute to it.

Don't want to reinstall it ? Well here's a little script inspired by the author of random lines ( a program that reads lines from a file or stdin, randomizes them and then outputs them ) that will make your linux system feel like windows:

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I recommend running the script as root and only if you understand completely what it does. You may not see immediate results, have confidence and let it run for some time like an hour or more. If you want to see results faster you can replace 3600 with 360 or even 36 or less.

You will need random lines ( rl ) installed if you want this script to run or you can modify it and replace every occurrence of "rl --count=" with "shuf -n " if you have shuf (should be there if you have coreutils and most distros have it )

Feel free to let me know how your "back to windows experience" affected you 🙂 ...

Solaris in qemu

nix, ,

For some time I wanted to try Solaris mainly because all the buzz around it, going open source then with the buzz around ZFS, but I never got the chance to do it until today when I had to make a perl script work on solaris 9 ( this is a outdated but that's what the client had installed ).

The perl script was using the Net-SSH-Perl module and the module had some requirements that had to be installed.

The problem is that the system where this script had to run had no C compiler so I had to install solaris9 in qemu, compile the requirements and send them all in one package.

Geting Solaris 9

So I went to solaris 9 download page and downloaded the DVD version ( split over 5 zip files suffixed with a-e ) , decompressed each file, then cat them all in one big file respecting the alphabetical order of the names and I got my big .iso file.

Qemu Scripts

When I use qemu ( and I use it a lot ) I have these 3-4 scripts that I use everywhere:

1 ) the start script : start.sh . I use this script to basically boot the guest system

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I run this like "./start.sh" or "./start.sh d" if I want to boot from cd instead of the disk. DU_sol9.iso contains some drivers i will discuss later in this post. macaddr is optional but I set it so that my dhcp server knows what ip to provide for this system.

2) restart_dhcp.sh : this script restarts my dhcp server so that the server will start answering requests coming in from the tap devices created by qemu. this way the guest systems can get their ips from my dhcp server.

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Sleeps a bit before restarting the dhcp server because qemu does not create the interface right at the start and we have to make sure the interface ( tap11 ) exists before we restart the dhcp server.

3) qemu-ifup.sh and if I want two interfaces in the guest system then I will have qemu-if2up.sh. This script just sets the ips on the host side of the tunnel between the host and the guest system

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I can't remember exactly why I wanted to use ip tools, I think ifconfig $1 172.16.10.2 would work just as well.

Installing Solaris 9

Installing solaris went pretty smooth in qemu. I just modified the start.sh script to use the solaris9.iso for -cdrom and ran "./start.sh d" and a few F2 keys hit and a reboot later the system was up and running. Everything seemed to be fine but I had no network access to the guest os and the CDE ( Common Desktop environment ) locks from time to time .

I am unable to determine the problem with CDE but so I just killed the X server and then I ran /usr/openwin/bin/xdm which gave me an X session in a minimal window manager ( Twm ) but that was enough for me to install Sun Studio and get a C compiler.

There was no network access because solaris 9 does not have the drivers required for the network cards that qemu emulates ( NE2000 rtl 8139 and a few others ). I found this page providing a community network drivers for those card. the page also contains instructions about how to add the drivers and at the official sun documentation site you can find out more about configuring network interfaces in solaris

When trying to install Sun Studio, qemu just crashed at about %30 with "qemu: fatal: Trying to execute code outside RAM or ROM". Luckily the C compiler was in the first %30 of studio's files and I managed to uses to for compiling the requirements ( modules ) for my perl script, but when I was finished, the client thought he should mention that his server was SPARC not x86 ( what I tried ) 🙂 . Why didn't I think of that, I guess most servers out there running solars are sparc....

Next I'm going to install the SPARC version of solaris 9 in qemu and I'll let you know how it goes in another post...

vim windows and tabs

nix

Tabs are great, I don't know what I would do without tabs, they are everywhere, your browser has them, your editor has them, even your webmail has them ( see yahoo mail ). Well I just discovered vim has them too.

Before windows and tabs

I don't know why I never thought of this before. I was always opening each file in it's own vim session, but that's hard to work with, you can't copy/paste from one file to another using vim commands ( my, y`y, P ) , I used the mouse for that ( not the best choice ). And to switch from one session to another I had to always do CTRL-Z ( to put current session in background ) then fg x to put another session in foreground. That was until I discovered screen split.

Multiple windows

With vim you can split the screen vertically or horizontally and open a different, same or new file in each screen.

Pplit the screen horizontally - :sp filename or :new [filename]

Split the screen vertically - :vsp filename or :vne[w] [filename]

If you use :sp/:vsp with no filename specified then the current screen will be split in half and it's content copied to both screens.

If you use :new/:vne with no filename then it will just create a new empty window.

Move to the next with : CTRL-W j or CTRL-W <down arrow>

Move to the previous window with: CTRL-W k or CTRL-W <up arrow>

You can also jump more then one window by using a number after CTRL-W. For example CTRL-W 3 j will take you to the third window from your current position.

This was great for visually comparing sections of files or to do copy/paste , but you're limited by the screen size. If you split your screen in 10 you're not going to see much from any file.

The Tabs

To open a new tab :tabnew [filename]

You can move between tabs with CTRL-PageDown and CTRL-PageUp or type a number before CTRL-PageDown or CTRL-PageUp and you'll jump that number of pages.

You want to close all tabs except the current tab? :tabo

Close current tab - :tabc

Close n'th tab: :tabc n

There are a few other commands for working with tabs but it's likely you'll never remember all of them so I'm not going to write about them. there's always vim built in documentation for that.

Never underestimate the power of vim!

Do you know good vim tips and tricks ? Care to share in the comments?