Bạch Vân Thành

Normally when we are able to connect to a FTP server. We can see the directory, browser the files, upload/download. But it has a situation which prevents us from listing directory. As the result, we got kick out from server.

This error somehow causes by Iptables. When I turned off iptables, I can list the file. When I stopped “iptable” daemon, it works as expected. I’m surely that I config iptable to allow connection on port 21.

If you encounters this problem is this article is right way for you. When I googled about this error, I found a solution here:

http://serverfault.com/questions/224591/iptables-lets-me-connect-by-ftp-but-i-cant-get-dir-listing

http://serverfault.com/questions/131635/iptables-how-to-allow-incoming-ftp-traffic

The solution I used to solve this problem is to add this rule to iptables:

1.iptables -A INPUT -p tcp –dport 21 -m state –state NEW,ESTABLISHED,RELATED -j ACCEPT

Actually, I just open the file /etc/iptables/iptables.rule and inject the rule there

2.Second, I load module modprobe nf_conntrack_ftp

modprobe nf_conntrack_ftp

Because of using Arch, I just open /etc/rc.conf and edit MODULES array like this:

MODULES=(nf_conntrack_ftp)

That’s all I got to get VsFtpd works again for me.

When you do cross-compiling, the compiler doesn’t know information of target platform such as: size of some data type, the const, flag, specification of compiler on that platform,..

For examples, you can got something like this:

check­ing for grow­ing stack pointer… con­fig­ure: error: can­not run test pro­gram while cross com­pil­ing
See ‘config.log’ for more details.
checking for posix getpwuid_r... (cached) yes
checking for posix getgrgid_r... configure: error: in `/8652_3110_tango/libraries/glib-2.20.4':

So we must let compiler know himself via a special cache file which can be specified via param –-cache-file when executing configure. If we name it config.cache then we do configure –cache-file=config.cache. Basically, we manually add defination for those value, flag, constm,…
You maybe to gooogle or read document of software which you are compiling carefully to find out name of those flags, consts. Reading any errors which you see, google them then append to the cache file

Mine looks like this when compiling glibc for SMP86xx chip (Use http://www.codesourcery.com/ toolchain)

ac_cv_func_posix_getpwuid_r=${ac_cv_func_posix_getpwuid_r=yes}
glib_cv_stack_grows=${glib_cv_stack_grows=no}
glib_cv_uscore=${glib_cv_uscore=no}

samba_cv_CC_NEGATIVE_ENUM_VALUES=yes
ac_cv_func_getpgrp_void=no
ac_cv_func_setpgrp_void=yes
ac_cv_func_memcmp_working=yes
rb_cv_binary_elf=no
rb_cv_negative_time_t=no

If you have enough C/C++ knowledge, you can easily find out the name of flag, definition and manually set value for them. Unfortunately, it can be not a simple job so just gooogle it or read docuement as I did .

So the idea is to manually define flags of target platform which current platform (compiler) doesn’t know about it. That’s all.

I hate SVN, you will not know how much I hate it. When think of fucking days with it, I always wonder how I can live on it. Nowadays, as long as I see SVN, i always keep away from it! Not like Mercurial or Git, SVN always keep a .svn folder in every directorys of your project! Of course I want to get rid of these stuffs! In the first part of my life, I always wrote bash script to do this task:

#!/bin/bash
value=0;

while read line
do
echo "rm -R  \"/home/kureikain/www/folio1/$line\""
rm  -R  /home/kureikain/www/folio1/$line
done < "svn-del"

echo $value;

Later I see some tutorials which use power of -exec param, It was really cool:

find . -name .svn -exec 'rm -rf {}\;'

Actually -exec is a powerful parameter which I will write about it in another article. Right now, we just go with above command to remove all svn stuff . After 3 years with Linux, I understand an important thing: my command line fu is really bad (!

I recently switch to other VPS! Becasue of this when I ssh to new VPS (with the same domain), I got this:

[lambasino@lambasino ~]$ ssh axcoto.com -l kureikain
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@       WARNING: POSSIBLE DNS SPOOFING DETECTED!          @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
The ECDSA host key for axcoto.com has changed,
and the key for the corresponding IP address 208.111.35.209
has a different value. This could either mean that
DNS SPOOFING is happening or the IP address for the host
and its host key have changed at the same time.
Offending key for IP in /home/lambasino/.ssh/known_hosts:4
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@
IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY!
Someone could be eavesdropping on you right now (man-in-the-middle attack)!
It is also possible that a host key has just been changed.
The fingerprint for the ECDSA key sent by the remote host is
fa:87:6d:54:d1:39:23:f6:78:fb:46:07:13:00:3a:1d.
Please contact your system administrator.
Add correct host key in /home/lambasino/.ssh/known_hosts to get rid of this message.
Offending ECDSA key in /home/lambasino/.ssh/known_hosts:1
ECDSA host key for axcoto.com has changed and you have requested strict checking.
Host key verification failed.
[lambasino@lambasino ~]$

So, it turns because of the different of key in old VPS and new VPS! Of course I must remove entry for axcoto.com in my known_hosts to force ssh add host key again!

I open vim and remove that line – line which start with axcoto.com!

But I think it must have some better way or more regular way instead of hard-coding it! It turns out very easy to do it! Just use

ssh-keygen but with -R switch!

[lambasino@lambasino ~]$ ssh-keygen -R axcoto.com
/home/lambasino/.ssh/known_hosts updated.
Original contents retained as /home/lambasino/.ssh/known_hosts.old

Remember to remove IP too if you used IP for connecting before!