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What is /dev/shm and its practical usage ?

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What is /dev/shm and its practical usage ?

/dev/shm is nothing but implementation of traditional shared memory concept. It is an efficient means of passing data between programs. One program will create a memory portion, which other processes (if permitted) can access. This will result into speeding up things on Linux.

If you type mount command you will see /dev/shm as a tempfs file system. Therefore, it is a file system, which keeps all files in virtual memory. Everything in tmpfs is temporary in the sense that no files will be created on your hard drive. If you unmount a tmpfs instance, everything stored therein is lost. By default almost all distro configured to use /dev/shm.

Nevertheless, where can I use /dev/shm?
You can use /dev/shm to improve the performance of application software or overall Linux system performance. On heavily loaded system, it can make tons of difference. For example VMware workstation/server can be optimized to improve your Linux host’s performance (i.e. improve the performance of your virtual machines).

For example, if you have 8GB RAM then remount /dev/shm as follows:

# mount -o remount,size=8G /dev/shm

To be frank if you have more than 2GB RAM and if you running multiple Virtual machines this hack always improves performance.

Fatal error: Allowed memory size of 123456 bytes exhausted (tried to allocate 234567 bytes) in /path/file.php

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Php is setup is to limit memory usage per process. If you require more, this limit can be increased.
Edit

/usr/local/lib/php.ini

If you are unsure about the php.ini path, You can find your server php.ini using command :

php -i | grep php.ini

Configuration File (php.ini) Path => /usr/local/lib

Loaded Configuration File => /usr/local/lib/php.ini

and set:

memory_limit = 8M ; Maximum amount of memory a script may consume (8MB)

to a higher value, like 20M. Save, exit, then restart apache.

DirectAdmin Apache won’t restart: [crit] (98)Address already in use: make_sock: could not bind to port 8090

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Apache won’t restart: [crit] (98)Address already in use: make_sock: could not bind to port 8090

[crit] (98)Address already in use: make_sock: could not bind to port 8090
or
[crit] (98)Address already in use: make_sock: could not bind to port 443
or
[crit] (98)Address already in use: make_sock: could not bind to port 80

If you see this error in your /var/log/httpd/error_log, it would mean that apache isn’t shutting down completely before trying to restart. This means that the new process won’t be able to bind to the given ports because they’re still being used by the old copy of apache that wasn’t completely shut down.

To solve this, use a different boot script that will wait for all apache processes to stop before starting the new one:

cd /usr/local/directadmin/customapache
rm -f httpd*
./build update

Once you have the new scripts downloaded, you need to install them:

RedHat:

cp httpd /etc/init.d/httpd
chmod 755 /etc/init.d/httpd
chkconfig httpd reset

FreeBSD:

cp httpd_freebsd /usr/local/etc/rc.d/httpd
chmod 755 /usr/local/etc/rc.d/httpd

Where can I change log permissions so other programs can read apaches web logs?

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Click on the “Tweak Settings” link under “Server Setup”. Within the “Stats and Logs” section is a text box with the heading:

“Chmod value for raw apache log files (0640 is the default):”

Change the value to suit your needs and apply the changes by clicking on the “Save” button at the bottom of the page.

Most programs only need read permissions on the log files so setting this to 0644 should suffice.

How to enable iconv on CPanel server?

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The iconv API is the standard programming interface for converting character strings from one character encoding to another in Unix-like operating systems. Initially appearing on the HP-UX operating system, it was standardized within XPG4 and is part of the Single UNIX Specification (SUS).

All recent Linux distributions contain a free implementation of iconv() as part of the GNU C Library which is the C library for current Linux systems. To use it, the GNU glibc locales need to be installed, which are provided as a separate package (usually named glibc-locale) normally installed by default.

…. source : wikipedia.org

From WHM you can compile Apache with iconv :

WHM Main >> Software >> EasyApache (Apache Update)

Follow the wizard and slect “Iconv (experimental)” under PHP Exhaustive Settings and start the Apache build by using “Start Build”.