Category: Troubleshoot

device-mapper: cache: You have created a cache device with a lot of individual cache blocks

The error would be similar to the following to be exact:

[172593.817178] device-mapper: cache: You have created a cache device with a lot of individual cache blocks (3276800)
[172593.817182] All these mappings can consume a lot of kernel memory, and take some time to read/write.
[172593.817185] Please consider increasing the cache block size to reduce the overall cache block count.

It usually appears because you have created a large cache pool, while using a small chunk size.

Here is what to be said about chunk size in lvmcache2 manual:

The size of data blocks managed by a cache pool can be specified with
the –chunksize option when the cache LV is created. The default
unit is KiB. The value must be a multiple of 32KiB between 32KiB and
1GiB.

Using a chunk size that is too large can result in wasteful use of
the cache, where small reads and writes can cause large sections of
an LV to be mapped into the cache. However, choosing a chunk size
that is too small can result in more overhead trying to manage the
numerous chunks that become mapped into the cache. Overhead can
include both excessive CPU time searching for chunks, and excessive
memory tracking chunks.

Basically chunk size is determining the block size at which your caches are going to be stored. To find your current chunk size run:

lvs -o+chunksize vgname/cachevolumename

Should return something like the following:

#lvs -o+chunksize vg0/newvz
LV VG Attr LSize Pool Origin Data% Meta% Move Log Cpy%Sync Convert Chunk
newvz vg0 Cwi-aoC— 1.50t [cache] 14.14 0.75 5.12 64.00k

A good chunk size for a large cache device of size 200GB+ would be 256k. You may set the chunk size while setting up the device :

lvcreate –type cache-pool –chunksize 256K -L CacheSize -n CachePoolLV VG FastPVs

How to create /var/cpanel/userdata files using /var/cpanel/users files

While reverting back from a reverse proxy like nginx/varnish installation, you might end up having an inconsistent /var/cpanel/userdata and /var/cpanel/users files. To be noted, /var/cpanel/userdata is used to create the httpd.conf file, while /var/cpanel/users are used to create the dns zone files. If you have an inconsistency between this two, you will have two different IP for named and httpd, which is undesirable. As the reverse proxy plays with /var/cpanel/userdata, which is why, we usually see the userdata folder containing incorrect data. Cpanel comes with a feature to reset userdata directory through it’s tools. Although, the tool uses a valid httpd.conf file or a backup to create userdata directory. Interestingly, if your httpd.conf isn’t valid that was created using an inconsistent userdata, can’t be used backward.

This is when you might require to create a /var/cpanel/userdata directory using the valid /var/cpanel/users directory. We ended up in this situation and written the following bash code to do the job for us:

#!/bin/sh

ls /var/cpanel/users/* > users.txt

while read line; do

UIP=$(grep “IP” /var/cpanel/users/$line|cut -d’=’ -f2)
sed -ie “/^ip: / c ip: $UIP” /var/cpanel/userdata/$line/*

#sed -i ‘/ip:/s/.*/ip: `echo $UIP`/’ /var/cpanel/userdata/$line/*

rm -f /var/cpanel/userdata/$line/*.cache

done < users.txt

 

The code deletes the cache files as well. Cpanel ships a script to rebuild the cache files, but for some reason it didn’t work for us. So we manually deleted the cache using rm. Please remember to backup the /var/cpanel/userdata and /var/cpanel/users directory before running the scripts.

Cpanel given cache rebuild command is:

/scripts/updateuserdatacache

Once the cache removal/build is completed, you may now rebuild your httpd conf file:

/scripts/rebuildhttpd.conf

service httpd restart

Backend log: PHP Warning: File upload error – unable to create a temporary file in Unknown on line 0

It is a common php error appears when PHP handler unable to detect the server temporary folder automatically. A solution to the problem is to define the upload_tmp_dir of the php explicitly. You can do that by editing the php.ini file. Here is an example on how to do it:

To find the running php.ini file, use phpinfo:

root@chicago1 [~]# php -r ‘phpinfo();’|grep php.ini
Configuration File (php.ini) Path => /opt/cpanel/ea-php56/root/etc
Loaded Configuration File => /opt/cpanel/ea-php56/root/etc/php.ini

As the command suggests, your php.ini file is located under the following:

/opt/cpanel/ea-php56/root/etc/php.ini

Now, edit the file using your favorite editor:
nano /opt/cpanel/ea-php56/root/etc/php.ini
Find the location of upload_tmp_dir, which is usually commented out like the following:

;upload_tmp_dir =

Uncomment it by removing the semicolon from front and define the temporary directory location:

upload_tmp_dir = /tmp

Restart your apache.

There is another way you can do it. To do this, go to WHM >> MultiPHP INI Editor >> Editor Mode >> Find upload_tmp_dir and edit it accordingly.

This would create a user.ini file to be included with the original php.ini file.

If none of the above solution works for you, you are probably seeing the error from modsecurity, try following the following steps to see if that overcomes the error:

ModSecurity: Multipart parsing error: Multipart: Failed to create file: /root/tmp/20170526-122120-WSfJYO2KhTvEz5johZF8UQAAAEw-file-9mmG15

ModSecurity: Multipart parsing error: Multipart: Failed to create file: /root/tmp/20170526-122120-WSfJYO2KhTvEz5johZF8UQAAAEw-file-9mmG15

If you are using ‘inspectFile’ of modsecurity, you may face an error in cpanel server like following

ModSecurity: Multipart parsing error: Multipart: Failed to create file: /root/tmp/20170526-122120-WSfJYO2KhTvEz5johZF8UQAAAEw-file-9mmG15

This error appears because mod_security fails to detect the tmp folder automatically. To fix the problem, all you need to add the following line in your modsec_user.conf file for cpanel servers:

SecTmpDir /tmp

This file is available under

/etc/apache2/conf.d/modsec

Alternatively, you may add the line from Cpanel >> Modsecurity Tools >> Add Rules.

‘ca-certificates’ update error

Since the last “ca-certificates” release for RHEL/CentOS 6 or Fedorar 14 with version stating 2013, there is a roaming error of not being able to update “ca-certificate” version starting from 2010 to the latest 2013. The error is somewhat looks the following through yum:

Running Transaction
Updating : ca-certificates-2013.1.94-65.0.el6.noarch 1/2
Error unpacking rpm package ca-certificates-2013.1.94-65.0.el6.noarch
warning: /etc/pki/java/cacerts created as /etc/pki/java/cacerts.rpmnew
warning: /etc/pki/tls/certs/ca-bundle.crt created as /etc/pki/tls/certs/ca-bundle.crt.rpmnew
warning: /etc/pki/tls/certs/ca-bundle.trust.crt created as /etc/pki/tls/certs/ca-bundle.trust.crt.rpmnew
error: unpacking of archive failed on file /etc/ssl/certs: cpio: rename
Verifying : ca-certificates-2013.1.94-65.0.el6.noarch 1/2
ca-certificates-2010.63-3.el6_1.5.noarch was supposed to be removed but is not!
Verifying : ca-certificates-2010.63-3.el6_1.5.noarch 2/2

Failed:
ca-certificates.noarch 0:2010.63-3.el6_1.5 ca-certificates.noarch 0:2013.1.94-65.0.el6

The following part of the error to be noted:

error: unpacking of archive failed on file /etc/ssl/certs: cpio: rename

It looks like the new “ca-certificate” is using a new structure. In old versions, “certs” is a folder which contains old certificates. While updating with the new one, it is trying to create a symlink with the /etc/pki/tls/certs/ by removing the old directory, which it fails with yum.

To solve the error, run the following:

$ mv /etc/ssl/certs /etc/ssl/certs.back
$ ln -s /etc/pki/tls/certs /etc/ssl/certs
$ yum update ca-certificate*

This should solve the error.