Netstat analysis for outgoing/incoming connections

netstat supports a set of options to display active or passive sockets. The options –t, –u, –w, and –x show active TCP, UDP, RAW, or Unix socket connections. If you provide the –a flag in addition, sockets that are waiting for a connection (i.e., listening) are displayed as well. This display will give you a list of all servers that are currently running on your system.

Invoking netstat -ta on vlager produces this output:

$ netstat -ta (you can also use -n option to avoid the dns lookup for displaying domain names, which will save performace).

Active Internet Connections
Proto Recv-Q Send-Q Local Address Foreign Address (State)
tcp 0 0 *:domain *:* LISTEN
tcp 0 0 *:time *:* LISTEN
tcp 0 0 *:smtp *:* LISTEN
tcp 0 0 vlager:smtp vstout:1040 ESTABLISHED
tcp 0 0 *:telnet *:* LISTEN
tcp 0 0 localhost:1046 vbardolino:telnet ESTABLISHED
tcp 0 0 *:chargen *:* LISTEN
tcp 0 0 *:daytime *:* LISTEN
tcp 0 0 *:discard *:* LISTEN
tcp 0 0 *:echo *:* LISTEN
tcp 0 0 *:shell *:* LISTEN
tcp 0 0 *:login *:* LISTEN

This output shows most servers simply waiting for an incoming connection. However, the fourth line shows an incoming SMTP connection from vstout, and the sixth line tells you there is an outgoing telnet connection to vbardolino.[1]

Using the –a flag by itself will display all sockets from all families.

Notes
[1]

You can tell whether a connection is outgoing from the port numbers. The port number shown for the calling host will always be a simple integer. On the host being called, a well-known service port will be in use for which netstat uses the symbolic name such as smtp, found in /etc/services.

Using vmstat for virtutal memory analyze

vmstat, as its name suggests, reports virtual memory statistics. It shows how much virtual memory there is, how much is free and paging activity. Most important, you can observe page-ins and page-outs as they happen. This is extremely useful.

To monitor the virtual memory activity on your system, it's best to use vmstat with a delay. A delay is the number of seconds between updates. If you don't supply a delay, vmstat reports the averages since the last boot and quit. Five seconds is the recommended delay interval.

To run vmstat with a five-second delay, type:

vmstat 5

You also can specify a count, which indicates how many updates you want to see before vmstat quits. If you don't specify a count, the count defaults to infinity, but you can stop output with Ctrl-C.

To run vmstat with ten updates, five seconds apart, type:

vmstat 5 10

Here's an example of a system free of paging activity:

procs memory swap io system cpu
r b w swpd free buff cache si so bi bo in cs us sy id
0 0 0 29232 116972 4524 244900 0 0 0 0 0 0 0 0 0
0 0 0 29232 116972 4524 244900 0 0 0 0 2560 6 0 1 99
0 0 0 29232 116972 4524 244900 0 0 0 0 2574 10 0 2 98

All fields are explained in the vmstat man page, but the most important columns for this article are free, si and so. The free column shows the amount of free memory, si shows page-ins and so shows page-outs. In this example, the so column is zero consistently, indicating there are no page-outs.

The abbreviations so and si are used instead of the more accurate po and pi for historical reasons.

Here's an example of a system with paging activity:

procs memory swap io system --- cpu ---
r b w swpd free buff cache si so bi bo in cs us sy id
. . .
1 0 0 13344 1444 1308 19692 0 168 129 42 1505 713 20 11 69
1 0 0 13856 1640 1308 18524 64 516 379 129 4341 646 24 34 42
3 0 0 13856 1084 1308 18316 56 64 14 0 320 1022 84 9 8

Notice the nonzero so values indicating there is not enough physical memory and the kernel is paging out. You can use top and ps to identify the processes that are using the most memory.

You also can use top to show memory and swap statistics. Here is an example of the uppermost portion of a typical top report:

14:23:19 up 348 days, 3:02, 1 user, load average: 0.00, 0.00, 0.00
55 processes: 54 sleeping, 1 running, 0 zombie, 0 stopped
CPU states: 0.0% user, 2.4% system, 0.0% nice, 97.6% idle
Mem: 481076K total, 367508K used, 113568K free, 4712K buffers
Swap: 1004052K total, 29852K used, 974200K free, 244396K cached

Apache Module mod_deflate

Looking to tune the apache for performance, then this should help you out.

The mod_deflate module provides the DEFLATE output filter that allows output from your server to be compressed before being sent to the client over the network


This is a simple sample configuration for the impatient.
Compress only a few types

AddOutputFilterByType DEFLATE text/html text/plain text/xml

The following configuration, while resulting in more compressed content, is also much more complicated. Do not use this unless you fully understand all the configuration details.
Compress everything except images


# Insert filter
SetOutputFilter DEFLATE

# Netscape 4.x has some problems...
BrowserMatch ^Mozilla/4 gzip-only-text/html

# Netscape 4.06-4.08 have some more problems
BrowserMatch ^Mozilla/4\.0[678] no-gzip

# MSIE masquerades as Netscape, but it is fine
# BrowserMatch \bMSIE !no-gzip !gzip-only-text/html

# NOTE: Due to a bug in mod_setenvif up to Apache 2.0.48
# the above regex won't work. You can use the following
# workaround to get the desired effect:
BrowserMatch \bMSI[E] !no-gzip !gzip-only-text/html

# Don't compress images
SetEnvIfNoCase Request_URI \
\.(?:gif|jpe?g|png)$ no-gzip dont-vary

# Make sure proxies don't deliver the wrong content
Header append Vary User-Agent env=!dont-vary

Subversion stress testing.

Today for one of my friend I've explored a new tool, which was used for stress testing on subversion.

You can find the script here.

Basically the script is for performing multiple operations on the repository to test the load.