Web services

PHP

Downgrading PHP 7 to PHP 5.6

• Last tested on Ubuntu 14.04.4 LTS (trusty) | easy | less than ten minutes

This should be also applicable for Ubuntu 16.04 (xenial) since it has PHP 7.0 as the default. I had temporarily upgraded to PHP 7.0 to check compatibility of one of our applications and Crypt_RSA package turned out to be the sore spot. So we had to revert back.

This may only apply for Ubuntu 14.04.4 or other versions less than 16.04. This is to add Ondřej Surý's PPA repository for PHP. Of course, if you have 14.04 and already have PHP 7.0, you probably have done this. If you don't have add-apt-repository, then please add it by adding a package called python-software-properties.

$ sudo apt-get install python-software-properties

Add repository for PHP

$ sudo add-apt-repository -y ppa:ondrej/php

Update package lists:

$ sudo apt-get update

Install PHP 5.6. You may also add other extensions you may need for your app (e.g. php5.6-mbstring, php5.6-xml, etc.)

$ sudo apt-get install php5.6

Switch the default PHP to PHP 5.6.

$ sudo update-alternatives --config php

Reference: Downgrade PHP 7 to PHP 5.6

enable PHP 5.6 FPM in apache2

$ a2enmod prox_fcgi setenvif
$ a2enconf php5.6-fpm

SSL/TLS

Generate a CSR

• Last tested on Ubuntu 14.04.2 LTS (trusty) | easy | less than five minutes

This will generate a 2048-bit key (secure & insecure) and CSR for usage on a website. CSR is short for Certificate Signing Request and is usually requested by CA (Certificate Authority) when trying to obtain a SSL/TLS certificate.

1. Create a secure key for CSR

$ openssl genrsa -des3 -out server.key 2048
Generating RSA private key, 2048 bit long modulus
.....................+++
....................+++
e is 65537 (0x10001)
Enter pass phrase for server.key:
Verifying - Enter pass phrase for server.key:

2. Create an insecure key for CSR sourcing from the secure one

$ openssl rsa -in server.key -out server.key.insecure
Enter pass phrase for server.key:
writing RSA key

3. Rename the keys

$ mv server.key server.key.secure
$ mv server.key.insecure server.key

4. Create the CSR

$ openssl req -new -key server.key -out server.csr

or

 $ openssl req -new -newkey rsa:2048 -nodes -keyout server.key -out server.csr
Generating a 2048 bit RSA private key
.............+++
..................+++
writing new private key to 'server.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [XX]:US
State or Province Name (full name) []:New Mexico
Locality Name (eg, city) [Default City]:Albuquerque
Organization Name (eg, company) [Default Company Ltd]:The University of New Mexico
Organizational Unit Name (eg, section) []:IT
Common Name (eg, your name or your server's hostname) []:oraapi02d.unm.edu
Email Address []:

Please enter the following 'extra' attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

Let's Encrypt

Let's Encrypt

Creating self-signed certificates (usually for SSL connection)

$ sudo a2enmod ssl
$ sudo service apache2 restart

$ sudo mkdir /etc/apache2/ssl

$ sudo openssl req -x509 -nodes -days 365 -newkey rsa:2048 -keyout /etc/apache2/ssl/apache.key -out /etc/apache2/ssl/apache.pem -outform PEM

Miscellaneous

Browsing on a console

• You can use the text-based web browser w3m to browse the Internet in your console screen. e.g 'w3m http://ubuntu.com'

Good resources for setting up mail servers

• Debian Mail Server with Postfix and Dovecot
• Debian Mail Server, Part II: SPF and DKIM

"No space left on device" error on a LAMP web server

• Tested on: Ubuntu 12.04 Precise
• Difficulty: 2/10
• Time: >10 minutes + number of files to delete + your WPM

If you try to create a blank file,

$ touch forcefsck
touch: cannot touch 'forcefsck': No space left on device

you get a report back saying there is no space left on device. However, when you check the disk space:

$ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/sda1        52G   28G   22G  58% /
udev            7.9G  4.0K  7.9G   1% /dev
tmpfs           3.2G  524K  3.2G   1% /run
none            5.0M     0  5.0M   0% /run/lock
none            7.9G  140K  7.9G   1% /run/shm

There is still 58% of disk space left, so something else is wrong. After googling about this, it turns out that my inode was running out. To check the number of inodes:

$ df -i
Filesystem      Inodes   IUsed   IFree IUse% Mounted on
/dev/sda1      3393040 3393020      20  100% /
udev           2050686     489 2050197    1% /dev
tmpfs          2052885     384 2052501    1% /run
none           2052885       2 2052883    1% /run/lock
none           2052885      47 2052838    1% /run/shm

inode stands for index node, which is an index for a file/folder/device/etc. in the Unix file system scheme.

To find out which folder is causing this massive hemorrhage of inodes:

$ sudo -s

$ cd /

$ for i in /*; do echo $i; find $i -type f | wc -l; done
(...)
/home
34293
/initrd.img
0
/initrd.img.old
0
/lib
14655
/lib64
0
/lost+found
0
/media
0
/mnt
0
/opt
1402
(...)

It looks like there is a lot of inodes in /var for some reason, now we need to narrow down to a specific directory:

$ for i in ./* ; do echo $i; find $i -type f | wc -l; done
(...)
./crash
1
./lib
3186175
./local
0
./lock
0
(...)

$ cd lib

$ for i in ./* ; do echo $i; find $i -type f | wc -l; done
(...)
./pam
6
./php5
3012602
./plymouth
1
(...)

You can check the number of files in any directory by issuing ls -l | wc -l but I couldn't even do this because there were millions of files that have accumulated over a year. These files had accumulated because PHP isn't doing the garbage collection. Your session.gc_probability may be set to 0. Change it to 1.

$ /usr/lib/php5/maxlifetime
24

It's 24 minutes. Now, here is the command to delete all of the older files.

$ find /var/lib/php5/ -type f -cmin +$(/usr/lib/php5/maxlifetime) -print0 -exec rm {} \;

This isn't necessary if you have the garbage collection enabled from the PHP configuration, but here is a cron job to run every hour as a root if this isn't caused by PHP.

$ crontab -e
0      /usr/bin/find /var/lib/php5/ -type f -cmin +$(/usr/lib/php5/maxlifetime) -print0 -exec /bin/rm {} \;

References

http://pim.famnit.upr.si/blog/index.php?/archives/172-Running-out-of-inodes,-no-space-left-on-device,-php-not-cleaning-sessions.html (accessed on July 30, 2012)