The Sysstat Suite of Resource Monitoring Tools
Sysstat is a sophisticated tool.
Sysstat contains the following tools related to collecting I/O and CPU statistics:
iostat
Displays an overview of CPU utilization, along with I/O statistics for one or more disk drives.
mpstat
Displays more in-depth CPU statistics.
Sysstat also contains tools that collect system resource utilization data and create daily reports based on that data.
These tools are:
sadc
Known as the system activity data collector, sadc collects system resource utilization information and writes it to a file.
sar
Producing reports from the files created by sadc, sar reports can be generated interactively or written to a file for more intensive analysis.
Tags: Monitoring, resource, Suite, Sysstat, Tools
Hugepages
When a process uses some memory, the CPU is marking the RAM as used by that process. For efficiency, the CPU allocate RAM by chunks of 4K bytes (it’s the default value on many platforms). Those chunks are named pages. Those pages can be swapped to disk, etc.
Since the process address space are virtual, the CPU and the operating system have to remember which page belong to which process, and where it is stored. Obviously, the more pages you have, the more time it takes to find where the memory is mapped. When a process uses 1GB of memory, that’s 262144 entries to look up (1GB / 4K). If one Page Table Entry consume 8bytes, that’s 2MB [ 262144 * 8 ] to look-up.
Most current CPU architectures support bigger pages (so the CPU/OS have less entries to look-up), those are named Huge pages (on Linux), Super Pages (on BSD) or Large Pages (on Windows), but it all the same thing.
Reference: http://wiki.debian.org
Tags: Hugepages
Regular Expressions are a feature of UNIX. They describe a pattern to match, a sequence of
characters, not words, within a line of text.
Here is a quick summary of the special characters used in the grep tool and their meaning:
^ (Caret) = match expression at the start of a line, as in ^A.
$ (Question) = match expression at the end of a line, as in A$.
\ (Back Slash) = turn off the special meaning of the next character, as in \^.
[ ] (Brackets) = match any one of the enclosed characters, as in [aeiou]. Use Hyphen “-” for a range, as in [0-9].
[^ ] = match any one character except those enclosed in [ ], as in [^0-9].
. (Period) = match a single character of any value, except end of line.
* (Asterisk) = match zero or more of the preceding character or expression.
\{x,y\} = match x to y occurrences of the preceding.
\{x\} = match exactly x occurrences of the preceding.
\{x,\} = match x or more occurrences of the preceding.
Tags: Expressions, Regular, Understanding
Exim Message-IDs and spool files
The message-IDs that Exim uses to refer to messages in its queue are mixed-case alpha-numeric.
Files in /var/spool/exim/msglog contain logging information for each message and are named the same as the message-id.
Files in /var/spool/exim/input are named after the message-id, plus a suffix denoting whether it is the envelope header (-H) or message data (-D).
Exim Basic information
Print a count of the messages in the queue:
root@localhost# exim -bpc
Print a listing of the messages in the queue (time queued, size, message-id, sender, recipient):
Print a summary of messages in the queue (count, volume, oldest, newest, domain, and totals):
root@localhost# exim -bp | exiqsumm
Print what Exim is doing right now:
Tags: exim, Files, Message-IDs, spool
Generating a Certificate Signing Request (CSR)
Whether you are getting a certificate from a CA or generating your own self-signed certificate, the first step is to generate a key.
To generate the keys for the Certificate Signing Request (CSR) run the following command from a terminal prompt:
# openssl genrsa -des3 -out server.key 1024
Generating RSA private key, 1024 bit long modulus
…………………++++++
…………………++++++
Enter pass phrase for server.key:
You can now enter your passphrase. For best security, it should at least contain eight characters. The minimum length when specifying -des3 is four characters. It should include numbers and/or punctuation and not be a word in a dictionary. Also remember that your passphrase is case-sensitive. Re-type the passphrase to verify. Once you have re-typed it correctly, the server key is generated and stored in the server.key file.
Tags: certificate, Generating, Request (CSR), Signing
