Test TCP and UDP with Netcap

Testing TCP connection

Create TCP listener:

$ nc -l 9999

Create TCP Client:

$ nc -vt 192.168.5.12 9999
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connected to 192.168.5.12:9999.

Testing UDP connection

Create UDP listener:

$ nc -ul 9999

Create UDP Client:

$ nc -vu 192.168.5.12 9999
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connected to 192.168.5.12:9999.

Test UDP Connection only:

$ nc -zvu 192.168.5.12 9999
Connection to 192.168.5.12 9999 port [udp/*] succeeded!

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Delete all files except one

For files:

find . ! -name 'file.txt' -type f -exec rm -f {} +

For directories:


find . ! -name 'directory' -type d -exec rm -rf {} +

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Start MySql

$ sudo /etc/init.d/mysqld start

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sysctl to change kernel system settings

To list all settings configurable in the /proc/sys/ directory:

/sbin/sysctl -a


To assign values to writable files in the /proc/sys/ directory:

sysctl -w [parameter] = [value]

Example:

sysctl -w kernel.sysrq="1"

This only works for testing purposes. Special settings within /proc/sys/ are lost when the 

machine is rebooted. To preserve custom settings, add them to the /etc/sysctl.conf file.

Each time the system boots, the init program runs the /etc/rc.d/rc.sysinit script.

This script contains a command to execute sysctl using /etc/sysctl.conf to determine the

values passed to the kernel.

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IPC Queues - ENOSPC (No space left on device) error

ENOSPC returns from msgget indicates that the system-wide maximum number of message queues has been reached.

Solution:

Change this limit editing:
/proc/sys/kernel/msgmni

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