Moodle:::: Coding error detected, it must be fixed by a programmer: Failed to unserialise data from file. Either failed to read, or failed to write.

Go to moodle folder and run the following command

php admin/cli/purge_caches.php

SETTING UP A LAN NETWORK in LUBUNTU using Webmin

SETTING UP A LAN NETWORK

In this module, we have created a Local Area Network.

Toolkit Used:

Workstation Operating System	Lubuntu 15.04
External Network Interface Cards	Quantity 1 Manufacturer TP-LINK Model Number TF-3200
Switches	Quantity 1 Manufacturer D-LINK Model Number DES-10008A

Below are the steps followed while setting up a LAN.

1.    Install DHCP Server:

Installedisc-dhcp-server to maintain server setup and configuration.

$ sudo apt-get install isc-dhcp-server.

2.    Install webmin:

            Installed webmin to configure and maintain theDHCP server.

a.     Installed required dependencies:

$ sudo apt-get install perl libnet-ssleay-perl libauthen-pam-perl libpam-runtime openssllibio-pty-perl apt-show-versions python.

b.     Downloaded Webmin:

$ wget http://prdownloads.sourceforge.net/webadmin/webmin_1.770_all.deb

c.     Installed Webmin:

$ sudo dpkg --install webmin_1.770_all.deb

3.    Renaming Network Cards

In the current workstation, eth1 is connected to the MSIT LANand eth0 is the external NIC which is going to be used for setting up a LAN for IS specialization purposes. So, for the better understanding and avoidconfusion, we have renamed eth1 to WAN and eth0 to LAN.

$ sudo leafpad /etc/udev/rules.d/70-persistent-net.rules

4.    DHCP & LAN Configuration

             I.        Editing Network Interfaces:

Edited the network interfaces in order to configure the eth0

$ sudo leafpad /etc/network/interfaces

           II.        Check IP Configuration

Check the IP Configuration  of both LAN and WAN after editing interfaces.

            $ sudo ifconfig

          III.        Listen for DHCP request

Because there is more than one network card in our workstation, we need to select the network card (WAN) on which our server will be listen for DHCP request.
$ sudo leafpad /etc/default/isc-dhcp-server.

         IV.        Configure the DHCP server’s config file

Edit the dhcp.conf file in order to make changes according to our convenience.

$ sudo nano /etc/dhcp/dhcpd.conf

           V.        Enable IP Forwarding

Edit the sysctl.conf file to forward packets from WAN to LAN.

Uncomment IPV4 packet forwarding line.

$ sudo nano /etc/sysctl.conf

         VI.        Login to Webmin

After configuring all our requirements, login to webmin (https://localhost:10000/) using root account.

        VII.        Add Firewall Rules

a.   Enable MASQUERADE(NAT):

·         Select Networking in the left menu bar.

·         Select the Linux firewall from the Networking drop down menu.

·         Configure the Linux Firewall such that it should do the network address translation for WAN interface.

·         So, select “Do network address translation on external interface” for WAN.

·         Select the “Setup firewall” finally.

b.   Save IP Table rules

After the above step, save the rules to iptables.up.rules file by clicking on ‘Apply changes’ in IP Tables.

c.   Observe IP Table Changes

Observe the changes made to the iptables.up.rules result in modification of /etc/network/interfaces file

$ sudo cat /etc/network/interfaces

d.   Activate Network Interfaces

Make sure that both LAN and WAN is up and running. If in case anyone of the interfaces is down, activate it before proceeding.

      VIII.        Listen to WAN Interface

         IX.        Start the DHCP Server

 

5.   Results:

Three personal workstations are connected to the switch which is connected the DHCP Server. The DHCP server automatically allocates IP Addresses to them.

IP address	WorkStation Name
192.168.0.11	Kittu
192.168.0.12	H3M4
192.168.0.13	HR

Details can be observed in the screenshot.

            It is the result of system log file (/var/log/syslog).

           

            $ sudo tail -50 /var/log/syslog

           

How to return multiple values from a C function

#include

void fun(int ,int ,int *,int *,int *);

int main()

{

int a=30,b=20,sum,sub,pro;

fun(a,b,&sum,&sub,&pro);

print("%d %d %d\n",sum,sub,pro);

return 0;

}

void fun(int x,int y,int *s,int *su,int *mu)

{

*s=x+y;

*su=x-y;

*mu=x*y;

}

Ex: 2

#include

int main()
{
    int a=3,b=5;
    
    int *c=&a, *d=&b;
    
    int sum,avg;
     
     fun(c,d,&sum,&avg);
     
    printf("%d %d",sum,avg);
    getch();
    
}

int fun(int *a, int *b, int *s, int *avg)
{
    *s=*a+*b;
    *avg=(*a+*b)/2;
}


---------------------------------------

#include <stdio.h>
#include <conio.h>

/* This function returns an array of N even numbers */
int* getEvenNumbers(int N){
    /* Declaration of a static local integer array */
    static int evenNumberArray[100];
    int i, even = 2;
    
    for(i=0; i<N; i++){
        evenNumberArray[i] = even;
        even += 2;
    }
    /* Returning base address of evenNumberArray array*/
    return evenNumberArray;
}

int main(){
   int *array, counter;
   array = getEvenNumbers(10);
   printf("Even Numbers\n");
   for(counter=0; counter<10; counter++){
       printf("%d\n", array[counter]);
   }
   
   getch();
   return 0;

} 

Can't create a workable moodledata directory in centos 7 for moodle

First, put all your web content data under /var/www/html/. However, Fedora does not allow Apache to write anything anywhere by default, unless you explicitly permit that. For that, proper file/directory permissions are required, but not enough. Fedora uses SELinux (Security Enhanced Linux) to provide more robust security, and it doesn't allow Apache to write anything by default too.

Now, for each file and/or directory which should be writable (for which you receive ... is not writableerrors) you should set unconfined_u:object_r:httpd_sys_rw_content_t:s0 SELinux label to tell SELinux that these files/directories are allowed to be modified by Apache. For example, to make/var/www/moodledata and /var/www/html/moodle/theme writable, you should run (you can use -R so that this lable is set recursively if these directories contain subdirectories which should be writable):

chcon -R unconfined_u:object_r:httpd_sys_rw_content_t:s0 /var/www/moodledata /var/www/html/moodle/theme

Now, you can run setenforce 1 and see if the webiste is working properly. This is the solution.

But, what about setenforce 0 command? This command changes SELinux mode into permissivemode. In this mode, SELinux doesn't prevent any activity and only generates error messages in system's audit logs. This is why you didn't receive error messages anymore. However, putting SELinux in permissive mode is NOT a proper solution to make things work, I used it to see if your problem is related to SELinux. And, setenforce changes SELinux mode temporarily (until next shutdown/reboot). setenforce 1changes the SELinux mode to the default one, which is enforcing mode in which SELinux does actually prevent un-allowed activities.

This is the workflow that I would suggest when setting up a new thing in Fedora:

1. Put SELinux into Permissive mode (setenforce 0)
2. Set up the system as you like and make sure that it works correctly as intended
3. Put SELinux back to Enforcing mode (setenforce 1)
4. See if your system is still working fine. If not, check for SELinux errors in system audit logs (/var/log/audit) and try to solve the errors appropriately (it usually involves changing file/directory SELinux lables, or changing SELinux boolean parameters). A more user friendly approach is to useSELinux Troubleshooter GUI application rather than inspecting audit logs. It shows SELinux related errors along with suggested solutions.

Notice that you can modify SELinux configuration file (/etc/selinux/config) to completely disable SELinux or permanently set it into Permissive mode, but please don't. While many will suggest it as a solution to SELinux related problems, it is more like removing the problem rather than a solution for itu. However, for a development system where security is not important, you might decide to do that (In that case, I would personally prefer using permissive mode rather than completely disabling SELinux, so that you can still know about SELinux permission erros). When you decided to deploy your web application to production servers, you should know how to properly configure SELinux so that your web application works correctly even when SELinux is in Enfrocing mode.

Re-enable graphical root-login on 12.04 LTS

sudo passwd root
sudo sh -c 'echo "greeter-show-manual-login=true" >> /etc/lightdm/lightdm.conf'

Root won't show up as a user, but "Login" will, which is how you manually log in with users not shown in the greeter.

Rebooted and then you should be able to login as root.


OR

First of all, you must set root 's password.

sudo passwd root
Enter new UNIX password:

Now you have root password. Now activate the root account:

sudo usermod -U root

Then you should allow lightdm, gdm or kdm to allow logging in as root.

To enable this:

In GDM

Edit /etc/gdm/custom.conf file and include AllowRoot=true.

In KDM

Edit /etc/kde4/kdm/kdmrc file and change AllowRootLogin=false for AllowRootLogin=true.

In LightDM

This procedure enables the "Other" menu, so you can type the username root and login. You must edit/etc/lightdm/lightdm.conf and add greeter-show-manual-login=true. Then reboot.

Others session managers have other methods to accomplish this.

As you have noticed I gave the instructions but by any circumstance you should not run the GUI as root. Murphy's Law says that it is likely that you mess up somehow and will be annoyed starting again.

I played around enough, how do I go back?

To disable root login just type:

sudo passwd -dl root

MAC based filtering in squid

MAC based filtering is useful for networks using DHCP to assign ip addresses to systems. As we know MAC is hard coded on NIC and can’t be changed but IP addresses assigned by DHCP may change on next ip assignment. This tutorial will help you to how to Configure Squid Proxy Server Mac Address Based Filtering.

If you do not have Squid installed, Go to below link for installing squid on CentOS/RHEL/Fedorasystems.

Install and Configure SQUID Proxy Server on CentOS/RHEL Linux

ACL rules are need to add in squid configuration file /etc/squid/squid.conf. Remember that squid Squid always applied first matching rules from top to down order and ignore other after matching any rule

1. Block All Sites For Single MAC Address

Following configuration will block all the sites to system having MAC address 01:23:45:AB:CD:EF.

Squid ACL Rule:

acl pcmac1 arp 01:23:45:AB:CD:EF
http_access deny pcmac1

2. Block Single Site for Single MAC Address

Following configuration will block www.example.com site to system having MAC address 01:23:45:AB:CD:EF.

Squid ACL Rule:

acl blocksite1 dstdomain www.example.com
acl pcmac1 arp 01:23:45:AB:CD:EF
http_access deny blocksite1 pcmac1 

3. Block All Sites for Multiple MAC Addresses

Following configuration will block all the sites to systems having MAC addresses 01:23:45:AB:CD:EF and AB:CD:EF:01:23:45.

MAC Addresses List

# cat /etc/squid/mac-addrs.lst
01:23:45:AB:CD:EF
AB:CD:EF:01:23:45

Squid ACL Rule:

acl pcmacs arp "/etc/squid/mac-addrs.lst"
http_access deny pcmacs

4. Block Single Site for Multiple MAC Addresses

Following configuration will block www.example.com to systems having MAC addresses 01:23:45:AB:CD:EF and AB:CD:EF:01:23:45.

MAC Addresses List

# cat /etc/squid/mac-addrs.lst
01:23:45:AB:CD:EF
AB:CD:EF:01:23:45

Squid ACL Rule:

acl blocksite1 dstdomain www.example.com
acl pcmacs arp "/etc/squid/mac-addrs.lst"
http_access deny blocksite1 pcmacs

5. Allow Specific Site for Single MAC Address

Following configuration will allow www.example.com to system having MAC address 01:23:45:AB:CD:EF and deny other sites.
Squid ACL Rule:

acl pcmac1 arp 01:23:45:AB:CD:EF
acl allowsite1 dstdomain www.example.in
http_access allow allowsite1 pcmac1
http_access deny pcmac1

6. Allow Multiple Sites for Single MAC Address

Following configuration will allow all sites added in /etc/squid/allowsites.lst to system having MAC address 01:23:45:AB:CD:EF and deny other sites.

Allowed Sites List

# cat /etc/squid/allowsites.lst
www.google.co.in
yahoo.com
in.yahoo.com

Squid ACL Rule:

acl pcmac1 arp 01:23:45:AB:CD:EF
acl allowsite1 dstdomain "/etc/squid/allowsites.lst"
http_access allow allowsite1 pcmac1
http_access deny pcmac1

7. Allow Specific Site for Multiple MAC Addresses

Following configuration will allow www.example.com to systems having MAC address 01:23:45:AB:CD:EF and and AB:CD:EF:01:23:45 and deny other sites.

MAC Addresses List

# cat /etc/squid/mac-addrs.lst
01:23:45:AB:CD:EF
AB:CD:EF:01:23:45

Squid ACL Rule:

acl blocksite1 dstdomain www.example.com
acl pcmacs arp "/etc/squid/mac-addrs.lst"
http_access allow blocksite1 pcmacs
http_access deny pcmacs

8. Allow Multiple Sites for Multiple MAC Addresses

Following configuration will allow all the sites listed in /etc/squid/allowsites.lst to all systems having MAC address listed in /etc/squid/mac-addrs.lst and deny other sites.

MAC Addresses List

# cat /etc/squid/mac-addrs.lst
01:23:45:AB:CD:EF
AB:CD:EF:01:23:45

Allowed Sites List

# cat /etc/squid/allowsites.lst
www.google.co.in
yahoo.com
in.yahoo.com

Squid ACL Rule:

acl pcmacs arp "/etc/squid/mac-addrs.lst"
acl allowsites dstdomain "/etc/squid/allowsites.lst"
http_access allow allowsites pcmacs
http_access deny pcmacs