fev 112019

On some of our development servers, we run many instances of the Apache httpd web server on the same system. By “many”, I mean 30 or more separate Apache instances, each with its own configuration file and child processes. This is not unusual on DevCamps setups with many developers working on many projects on the same server at the same time, each project having a complete software stack nearly identical to production.

On Red Hat Enterprise Linux 5, with somewhere in the range of 30 to 40 Apache instances on a server, you can run into failures at startup time with this error or another similar one in the error log:

[error] (28)No space left on device: Cannot create SSLMutex

The exact error will depend on what Apache modules you are running. The “space left on device” error does not mean you’ve run out of disk space or free inodes on your filesystem, but that you have run out of SysV IPC semaphores.

You can see what your limits are like this:

# cat /proc/sys/kernel/sem
250 32000 32 128

I typically double those limits by adding this line to /etc/sysctl.conf:

kernel.sem = 500 64000 64 256

That makes sure you’ll get the change at the next boot. To make the change take immediate effect:

# sysctl -p

With those limits I’ve run 100 Apache instances on the same server.

out 072015

cPanel logs most activity that happens on a server to log files so you can go back and review log entries for problems, instead of having to be on the server at the time of them happening.

This guide will cover the locations of the log files for things such as access logs, Apache web server logs, email logs, error logs, ftp logs, MySQL logs, and WHM logs.

If you’d like to have a poster of the 2013 cPanel logs location reference, you can request them from cPanel directly.

You can also view a digitial copy of this poster directly online at go.cPanel.net/logposter.

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Install NTOP on Debian and Configure to Use NetFlow on Mikrotik RouterOS

 Apache2, Clusterweb, Leitura Recomendada, Linux, Mikrotik, Profissional de TI, Redes, Segurança  Comentários desativados em Install NTOP on Debian and Configure to Use NetFlow on Mikrotik RouterOS
jun 182014

Ntop is a network monitoring tool similar to Unix top, which shows network traffic usage. It can act as a NetFlow collector for flows generated by routers such as Cisco or Mikrotik. NetFlow is an industry standard for flow-based traffic monitoring.

We will install and configure Ntop to collect flows generated by Mikrotik router. Note: “Ntop” != “NtopNG”.

Install Pre-required Software

We’re using Debian Wheezy:

$ uname -rv
3.2.0-4-686-pae #1 SMP Debian 3.2.51-1

Update the system first:

# apt-get update && apt-get upgrade -uV

Install required software:

# apt-get install libtool automake autoconf make build-essential python-dev subversion

Install external tools and libraries required by ntop:

# apt-get install libpcap-dev libgdbm-dev zlib1g-dev libgeoip-dev libgraphviz-dev \
> graphviz rrdtool librrd-dev

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