Posts Tagged ‘CentOS’

Passive Mode FTP with iptables

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There’s lots of advice on the net about how to setup a server with iptables to allow passive mode FTP. Below is the approach that we’ve found to be most effective.

Start by configuring your FTP daemon to use a fixed range of ports. We use 41361 to 65534 which is the IANA registered ephemeral port range. The exact config depends on what FTP software you’re using:


Edit /etc/vsftpd/vsftpd.conf and add the following lines:



Edit /etc/proftpd.conf and add to the Global section:

PassivePorts 49152 65534

Now restart your FTP service so the changes take effect.

Next you’ll need to configure the ip_conntrack_ftp iptables module to load. On Redhat/CentOS just edit /etc/sysconfig/iptables-config and add “ip_conntrack_ftp” to the IPTABLES_MODULES like this:


Next edit /etc/sysconfig/iptables and add a rule to allow TCP port 21.
The new line is marked in red:

-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 21 -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 22 -j ACCEPT
-A INPUT -m state --state NEW -m tcp -p tcp --dport 80 -j ACCEPT
-A INPUT -j REJECT --reject-with icmp-host-prohibited
-A FORWARD -j REJECT --reject-with icmp-host-prohibited

Now restart the iptables service:

/sbin/service iptables restart

You can verify that the correct port range has been registered with lsmod like this:

lsmod | grep conntrack_ftp

and you’ll get something like this:

nf_conntrack_ftp       12913  0 
nf_conntrack           79645  4 nf_conntrack_ftp,nf_conntrack_ipv4,nf_conntrack_ipv6,xt_state

And that’s all it takes to get passive mode ftp working behind iptables.

P.S: If your server is behind a physical firewall and you are behind NAT, then you’ll probable need to load the “ip_nat_ftp” iptables module.

FTP automation on Linux

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Ever wanted FTP backups and automation for keeping backups of important file on off-peak time. I always love automation, so machines can do things automatically and help humans 🙂 Read the rest of this entry »

Mount point busy or already mounted error – CentOS



Recently when my servers HDD dead, data center installed a new HDD keeping orginal HDD as secondary so that i can copy data back to new HDD.

I tried to mount the HDD normal way, but got the error:-

[root@server78 ~]# fdisk -l /dev/hda
 Disk /dev/hda: 160.0 GB, 160041885696 bytes
 255 heads, 63 sectors/track, 19457 cylinders
 Units = cylinders of 16065 * 512 = 8225280 bytes
    Device Boot      Start         End      Blocks   Id  System
 /dev/hda1   *           1          13      104391   83  Linux
 /dev/hda2              14       19457   156183930   8e  Linux LVM
 [root@server78 ~]# mount /dev/hda2 /tmp/mnt
 mount: /dev/hda2 already mounted or /tmp/mnt busy

The old drive is lvm. you were trying to mount it like it was an ext3 filesystem. I have listed what i did below so you can see it.

Now we need to check the old disk is using LVM ? type:-

[root@server78 ~]# pvs
PV         VG         Fmt  Attr PSize   PFree
/dev/hda2  VolGroup01 lvm2 a-   148.94G 32.00M
/dev/hdb2  VolGroup00 lvm2 a-   114.94G 96.00M

So now we know our second hard disk VolumeGroup name is “VolGroup00”, now we can mount it like:-

[root@server78 ~]# mount /dev/VolGroup01/LogVol00 /mnt

That’s it, you can see the folders in /mnt/, Edit/copy as you like.

no “setup” command – CentOS



I usually use “setup” to do the firewall setup for permissive or not and setting of SELINUX, etc….

But on a minimal install you don’t have access to setup command, which is my favorite

[root@tel ~]# setup
-bash: setup: command not found

So how to install it in minimal install ?

yum –y install setuptool
yum –y install system-config-network*
yum -y install system-config-firewall*
yum –y install system-config-securitylevel-tui
yum –y install system-config-keyboard

(thanks JoVeN for spell mistake)

For system services utility install ntsysv (as Perico suggested in the user comments)

yum -y install ntsysv


That’s it….!! Enjoy

How To Download a RPM Package Using yum Command Without Installing On Linux

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If you ever wanted to download the rpm package instead of installing it with yum ! you can do that with ease, that is useful when you want to keep backup of some RPMs or want to see what’s inside RPM etc.
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Install XWindows (Graphical mode) in Linux



If you recently installed linux (CentOS/Fedora/RedHat) with text mode and now want to use its Graphical GUI which was left unchecked during the installation, you can install it from Internet very easily.

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