configure: error: *** zlib.h missing

Issue :

I got the above error when i try to upgrade openssh on the server.

Solution :

You can correct it by installing “zlib-devel” using the following command.

yum install zlib-devel

That’s all…!!!

configure: error: *** libwrap missing

Issue :

I got the above error when i try to upgrade openssh on the server.

Solution :

You can correct it by installing “tcp_wrappers-devel” using the following command.

yum install tcp_wrappers-devel

That’s all…!!!!

configure: error: PAM headers not found

Issue :

I got the above error when i try to upgrade openssh on the server.

Solution :

You can correct it by installing “pam-devel” using the following command.

yum install pam-devel

That’s all…!!!

Clear /tmp using tmpwatch

Tmpwatch tool is analyze and recursively delete files which have not been used certain period of time, especially clean up unwanted backup or /tmp directory or unused files.

When changing directories, tmpwatch is very sensitive to possible race conditions and will exit with an error if one is detected. It does not follow symbolic links in the directories it’s cleaning (even if a symbolic link is given as its argument), will not switch filesystems, and only removes empty directories and regular files.

Installation of tmpwatch

——————-

You can install tmpwatch on your linux server with simple commands.

CentoOS/Fedora/RHCE :

yum install tmpwatch -y

Ubuntu:

sudo apt-get install tmpreaper

Once it’s installed, you can find the tmpwatch Installed Location uisng the following command.

 whereis tmpwatch

 

OPTIONS

-u, –atime

Make the decision about deleting a file based on the file’s atime (access time). This is the default.

-m, –mtime

Make the decision about deleting a file based on the file’s mtime (modification time) instead of the atime.

-c, –ctime

Make the decision about deleting a file based on the file’s ctime (inode change time) instead of the atime; for directories, make the decision based on the mtime.

-a, –all

Remove all file types, not just regular files and directories.

-d, –nodirs

Do not attempt to remove directories, even if they are empty.

-f, –force

Remove files even if root doesn’t have write access (akin to rm -f).

 

Commands using tmpwatch

———————-

1. To cleanup /tmp directory files that haven’t been accessed for at least 30 days.

tmpwatch 30d /tmp/

2. To delete all /tmp files and directories over 12 hours old

tmpwatch -am 12 /tmp

3.To delete all the files only  that haven’t been accessed for at least 30 hours.

 tmpwatch -am  30 –nodirs /tmp

We can also set cron jobs to run the same automatically by server. You can add the cron job like pasted below sing your cPanel or as root user.

 0 4 * * * /usr/sbin/tmpwatch -am 12 /tmp

That’s all….!!!

Installing and configuring Spamassassin on CentOS server

If you run your own mail server you’ll want it to run spam filtering software to reduce the number of unsolicited emails your users receive.  SpamAssassin is an effective spam filter that’s relatively easy to install and run.

Installation

—————

The first thing we will want to do is run an update on our CentOS distribution if we haven’t already.

      yum update

Once the distribution has been updated, we will want to install SpamAssassin using yum.

     yum install spamassassin

Now that we have installed SpamAssassin onto our mail server we will need to configure the SpamAssassin rules within the local.cf file to set filter preferences.

Each item of email sent to your domain is given a score by SpamAssassin.  This score depends on characteristics of the email like keywords and attachments. As with any anti-spam engine, SpamAssassin will need training to become a more accurate filter to cater to your needs.

Configuration

—————–

Let’s take a look at the default configuration for the local.cf file within SpamAssassin.  To do this we will need to open the file and make some changes.  Please use your favoured text editor; in this example we will use nano.

      nano /etc/mail/spamassassin/local.cf

We will need to uncomment the following lines and append the score:

            required_hits 5.0
            report_safe 0
            required_score 5
            rewrite_header Subject ***SPAM***

To explain what we are doing and why we are doing this, we will need a short run-down on the above lines.

Required_hits: This determines the filter balance; the lower the score the more aggressive the filter. A setting of 5.0 is generally effective for a small organisation or a single user. Adjust the strictness score to your organization’s needs – a large medical organisation might want to let email items through that are trying to sell pharmaceuticals, so we might increase the level to a more modest 8.0.

Report_safe: This line determines whether to delete the item or to move the item to the inbox whilst appending a spam notice to the subject line. The levels for this line are set to either a 1 or 0. A score of 1 will delete the spam item, whereas a score of 0 will send the item to the inbox and rewrite the subject line. For this guide we shall use 0 as the score.

Required_score: This line sets the spam score for all email alllowed through to your domain, with levels of certainty set from 0 to 5. Zero would be classified as a legitimate email item, whereas 5 would be an definite ‘SPAM’ item. If we set the score to 3 we would catch a lot of unsolicited emails but quite a few false positives would still get through. For our example email server we will use the score of 5, but you can of course set this value according to your preference.

Rewrite_header: This line does exactly what it implies, that is, any message caught as ‘SPAM’ will have the subject line rewritten to include this header. For this guide we will use the default subject header of ***SPAM***.

Now that we have the spam variables set up we will now move on to creating the spamd function.

Spamd Setup

—————

Spamd and spamc are two functions that are necessary for SpamAssassin to work correctly. Spamd is the more proactive of the two functions; it lays in wait for incoming requests, acting as a daemon to intercept and process emails. Once spamd receives a connection it will spawn a spawnc child to read the email item from the network socket. This child will pass the message back to spamd when it reaches an end of file (EOF), which will rewrite the message (if you have SpamAssassin setting the subject header for spam). This email message will then be passed back to the socket it originally arrived on using the child process it spawned at the start. The child process will then end and your regular mail server will process the message.

In briefer terms: The spamd process and its children intercept all incoming messages and process them before your regular mail server ever sees them.

Because of the nature of spamd we will need to create a unique user and group for it so we can integrate Postfix with SpamAssassin. This can be done using commands in BASH:

               groupadd spamd
               useradd -g spamd -s /bin/false -d /var/log/spamassassin spamd
               chown spamd:spamd /var/log/spamassassin

Right, so now that we have the SpamAssasin local.cf file configured along with spamd we will need to configure the Postfix master.cf file to use the SpamAssassin scripts and the set scores we have just applied.

Postfix
We now need to access the Postfix master.cf file with a text editor.

       nano /etc/postfix/master.cf

We should now change the master.cf file to look as follows:

# ====================================================================
# service type private unpriv chroot wakeup maxproc command + args
# (yes) (yes) (yes) (never) (100)
# ====================================================================
smtp inet n – n – – smtpd -o content_filter=spamassassin

At the bottom of this file we should add the following line:

spamassassin unix – n n – – pipe flags=R user=spamd argv=/usr/bin/spamc -e /usr/sbin/sendmail -oi -f ${sender} ${recipient}

Before initially starting the SpamAssassin service run sa-update from a cronjob to update the spamd with the latest rules.

      sa-update && /etc/init.d/spamassassin reload

We should now start the SpamAssassin service and reload the Postfix service, to do this we can run the following commands:

        /etc/init.d/postfix reload

        /etc/init.d/spamassassin reload

To check the spam service is operating correctly we can try running a test.

The Test

———–

Create an email from an email address and service outside of your domain, e.g. Hotmail or Gmail. Address the email to an email address on the newly-configured mail server, then within the subject line we can use the following test string:

XJS*C4JDBQADN1.NSBN3*2IDNEN*GTUBE-STANDARD-ANTI-UBE-TEST-EMAIL*C.34X

Once this email has been fired off, and if all the settings have been entered correctly, we should be able to see the following message in our inbox:

****SPAM****XJS*C4JDBQADN1.NSBN3*2IDNEN*GTUBE-STANDARD-ANTI-UBE-TEST-EMAIL*C.34X

Success! We have now set up our server to use SpamassAssin to filter our inbound emails!

That’s all…!!!

Extending Swap space on an LVM

Sometimes it is necessary to add more swap space after installation. For example, you may upgrade the amount of RAM in your system from 1 GB to 2 GB, but there is only 2 GB of swap space. It might be advantageous to increase the amount of swap space to 4 GB if you perform memory-intense operations or run applications that require a large amount of memory.

You have three options: create a new swap partition, create a new swap file, or extend swap on an existing LVM2 logical volume. It is recommended that you extend an existing logical volume.

To do so, perform the following procedure (assuming /dev/VolGroup00/LogVol01 is the volume you want to extend by 2 GB):

1.Disable swapping for the associated logical volume:

# swapoff -v /dev/VolGroup00/LogVol01

2.Resize the LVM2 logical volume by 2 GB:

# lvresize /dev/VolGroup00/LogVol01 -L +2G

3.Format the new swap space:

# mkswap /dev/VolGroup00/LogVol01

4.Enable the extended logical volume:

# swapon -v /dev/VolGroup00/LogVol01

To test if the logical volume was successfully extended, use “cat /proc/swaps” or “free -m” to inspect the swap space.

Openvz “Container already locked”

Issue : When I try to restart a openvz vps , i got the error “Container already locked”

[root@server ~]# vzctl restart 1005

Container already locked

Solution:

Delete the /vz/lock/VEID.lck file

i.e;

#rm  /vz/lock/1005.lck

Then kill the check point.

#vzctl checkpoint 1005 –kill

Try to restart it now.

If the above solution doesn’t help,please use the following steps.

#vzquota off 1005

Or

#vzqouta drop 1005

Try to restart it now.

That’s all……!!!