Security Tip: Find Out Current Working Directory Of A Process Running on Linux/Unix

Posted on in Categories CentOS, Howto, Linux, Monitoring, RedHat/Fedora Linux, Security, Suse Linux, Sys admin, Tips, Ubuntu Linux last updated November 14, 2007

For security reason you may need to find out current working directory of a process. You can obtained this information by visiting /proc/pid/cwd directory or using the pwdx command. The pwdx command reports the current working directory of a process or processes.

How to: Debug SSL certificate problems from the shell prompt

Posted on in Categories Apache, Howto, Linux, Security, Shell scripting, Sys admin, Tips, Troubleshooting, UNIX last updated October 18, 2007

OpenSSL is a cryptography toolkit implementing the Secure Sockets Layer (SSL v2/v3) and Transport Layer Security (TLS v1) network protocols and related cryptography standards required by them.

It also includes the openssl command, which provides a rich variety of commands You can use the same command to debug problems with SSL certificates.

To test the secure connections to a server, type the following command at a shell prompt:
openssl s_client -connect

  • s_client : This implements a generic SSL/TLS client which can establish a transparent connection to a remote server speaking SSL/TLS. It’s intended for testing purposes only and provides only rudimentary interface functionality but internally uses mostly all functionality of the OpenSSL ssl library. You can also connect to secure mail server (such as POP3S ~ 995) / web server port (443) and issue commands.

For example connect to at port 443, enter:
openssl s_client -connect

depth=0 /C=IN/ST=Berkshire/L=Newbury/O=My Company Ltd/CN=*[email protected]
verify error:num=18:self signed certificate
verify return:1
depth=0 /C=IN/ST=Berkshire/L=Newbury/O=My Company Ltd/CN=*[email protected]
verify return:1
Certificate chain
 0 s:/C=IN/ST=Berkshire/L=Newbury/O=My Company Ltd/CN=*[email protected]
   i:/C=IN/ST=Berkshire/L=Newbury/O=My Company Ltd/CN=*[email protected]
Server certificate
subject=/C=IN/ST=Berkshire/L=Newbury/O=My Company Ltd/CN=*[email protected]
issuer=/C=IN/ST=Berkshire/L=Newbury/O=My Company Ltd/CN=*[email protected]
No client certificate CA names sent
SSL handshake has read 1066 bytes and written 316 bytes
New, TLSv1/SSLv3, Cipher is AES256-SHA
Server public key is 1024 bit
Compression: NONE
Expansion: NONE
    Protocol  : TLSv1
    Cipher    : AES256-SHA
    Session-ID: 989C62FBF87884C9F6904DD216A9A36189BE660059F419DAA16711AF2A7F42D4
    Master-Key: 9A01374F14D7300E8DD02BE2AA3C3567F26E1BB00267D5AB0156C6C11A10EB0D8424FBD06D3B15013B4FBA0F121EC99D
    Key-Arg   : None
    Start Time: 1192732059
    Timeout   : 300 (sec)
    Verify return code: 18 (self signed certificate)

Using grep you can see the SSL and TLS connection handshaking, security negotiate, public keys and transfer of digital certificates and key information to the client:
$ openssl s_client -state -nbio -connect 2>&1 | grep "^SSL"

SSL_connect:before/connect initialization
SSL_connect:SSLv2/v3 write client hello A
SSL_connect:error in SSLv2/v3 read server hello A
SSL_connect:SSLv3 read server hello A
SSL_connect:SSLv3 read server certificate A
SSL_connect:SSLv3 read server done A
SSL_connect:SSLv3 write client key exchange A
SSL_connect:SSLv3 write change cipher spec A
SSL_connect:SSLv3 write finished A
SSL_connect:SSLv3 flush data
SSL_connect:error in SSLv3 read finished A
SSL_connect:error in SSLv3 read finished A
SSL_connect:SSLv3 read finished A
SSL handshake has read 1066 bytes and written 316 bytes

Further readings:

=> OpenSSL man pages and documentation.

Quick Shell Tip: Remove grep command while grepping something using ps command

Posted on in Categories Linux, Shell scripting, Tip of the day, UNIX last updated October 15, 2007

Generally you use ps command to find out all running process. You may also pipe out ps command output via grep command to pickup desired output.

Basically you don’t want display grep command as the process.

Let us run combination of ps and grep command to find out all perl processes:
$ ps aux | grep perl

vivek      4611  0.0  0.7  10044  6068 ?        Ss   02:40   0:00 /usr/bin/perl apps/monitor/
root      4853  0.0  0.7  10044  6068 ?        Ss   02:40   0:00 /usr/bin/perl /usr/share/webmin/ /etc/webmin/miniserv.conf
vivek      5166  0.0  0.0   2884   748 pts/0    R+   03:06   0:00 grep perl

In above example you are getting the grep process itself. To ignore grep process from output, type any one of the following:
$ ps aux | grep perl | grep -v grep
$ ps aux | grep '[p]erl'

Quick tip: Easily find strings with grep color highlighting feature

Posted on in Categories Linux, Shell scripting, Sys admin, Tips, UNIX last updated October 11, 2007

grep command is the de facto tool for searching text files. However when there are too many matches, it can be difficult to find the requested text in the search results. grep comes with –color=’auto’ option. It surrounds the matching string with the colour, thus resulting enhanced output.

Finding string with color highlighting

Pass –color option to grep command:
# grep --color='auto' -i error /var/log/messages

Oct  9 16:12:14 vivek-desktop kernel: [   11.555442] bt878: probe of 0000:05:00.1 failed with error -22
Oct 10 17:35:28 vivek-desktop kernel: [   10.564710] bt878: probe of 0000:05:00.1 failed with error -22
Oct 11 10:15:34 vivek-desktop kernel: [   12.187477] bt878: probe of 0000:05:00.1 failed with error -22
Oct 11 14:29:56 vivek-desktop kernel: [   11.135309] bt878: probe of 0000:05:00.1 failed with error -22

Now all matched text displayed using red color. The –color option to matches in the input in red color by default. Color is added via ANSI escape sequences. To change color use environment variable GREP_COLOR. Following will set background to red and foreground to white:
$ export GREP_COLOR='1;37;41'
$ egrep --color=auto -i '(error|fatal|warn|drop)' /var/log/messages

Quick tip: Easily find strings with gep color highlighting feature
I recommend putting following in ~/.bash_profile OR ~/.bashrc file:
$ vi ~/.bash_profile
Append following alias:
export GREP_COLOR='1;37;41'
alias grep='grep --color=auto'

Save and close the file. Please note that –color option works with many GNU text utilities, so feel free to use the same.

Search Linux / UNIX log files smartly for an alert or warning error

Posted on in Categories CentOS, Debian Linux, Gentoo Linux, Howto, RedHat/Fedora Linux, Suse Linux, Sys admin, Troubleshooting, UNIX last updated September 26, 2007

So how do you find an alert or warning words in a log file over text based session? Simply use old good grep command. Usually I recommend searching following words
=> fail
=> denied
=> segfault
=> segmentation
=> rejected
=> oops
=> warn

Find an alert or warning words from log files

You need to use grep command:
grep {search-word} /path/to/log/file

Find out all segfault error from /var/log/messages file, enter the following command as privileged user:
# grep -i segfault /var/log/messages

Sep 23 12:20:09 node10 kernel: mutt[8896]: segfault at 0000000000000010 rip 0000000000439d5e rsp 00007fff36a30040 error 6
Sep 24 12:20:10 node10 kernel: mutt[20107]: segfault at 0000000000000010 rip 0000000000439d5e rsp 00007fffd99dbac0 error 6
Sep 25 12:20:09 node10 kernel: mutt[19734]: segfault at 0000000000000010 rip 0000000000439d5e rsp 00007fff5d807290 error 6

Look like node10’s mutt command generated segfault error while sending daily reports attachment via email.

GUI Tools

System Log Viewer is a graphical, menu-driven viewer that you can use to view and monitor your system logs. System Log Viewer comes with a few functions that can help you manage your logs, including a calendar, log monitor and log statistics display.

Redhat / CentOS tool

Redhat (RHEL) Linux offers gui tool called Log Viewer. Type the redhat-logviewer command at a shell prompt or use GUI menus to start the same. You can set filter words (alter words) by clicking on Edit > Preferences menu > Alter tab > Add button

Debian / Ubuntu tool

Debian / Ubuntu Linux also offers GUI tool to view and search log files by setting filters. Click on Applications menu > Choose System Tools > Admin > System Log.
Debian / Ubuntu Linux also offers GUI tool to view and search log files by setting filters

Linux tip: Save Power With Gigabit Ethernet By Using Lower Speed

Posted on in Categories Howto, Linux, Sys admin, Tips, UNIX last updated September 21, 2007

This is a reader contributed article.

These days almost all server / laptop / desktop system has a gigabit Ethernet card (NIC) pre installed. Most servers are directly connected to internet using 100Mbps connections. You can save real power on your Linux server or desktop by operating at 100Mbps Ethernet speed. For example 1 gigabit link is going to consume more power than the power used at 100Mbps speed. Also note that not all systems actually use gigabit speed. For example my desktop system only used for browsing or chatting purpose or Linux web server used to display just static web pages. Now just calculate power consumption for 100 servers or 1000 desktop systems. Bottom line use Gigabit Ethernet speeds only when needed. Did you know – you can save 2 watts or more per Linux/UNIX/Windows server/desktop by just setting a correct speed 🙂

See current Ethernet card speed

Use ethtool comment to display current speed:
ethtool eth0 | grep -i speed

Set new speed and save power

Following command will set card speed to 100Mbps:
ethtool -s eth0 autoneg off speed 100

=> For more information see ethtool command and network interface speed, duplex . auto negotiate settings on Linux

About the author: Rocky Jr., is an engineer with VSNL – a leading ISP / global telecom company in India and a good friend of nixCraft.

Linux: Find Out How Many File Descriptors Are Being Used

Posted on in Categories File system, Linux, Sys admin, Tips, Troubleshooting last updated August 21, 2007

While administrating a box, you may wanted to find out what a processes is doing and find out how many file descriptors (fd) are being used. You will surprised to find out that process does open all sort of files:
=> Actual log file

=> /dev files

=> UNIX Sockets

=> Network sockets

=> Library files /lib /lib64

=> Executables and other programs etc

In this quick post, I will explain how to to count how many file descriptors are currently in use on your Linux server system.

Domain Expiration Check Shell Script

Posted on in Categories Howto, Shell scripting, Tip of the day, Tips last updated August 31, 2017

I have already written a shell script to check/monitor domain renew / expiration date here. Now I have modified matty’s domain-check script to support additional C/TLDs .in, .biz, .org and .info domains. I’ve also added 5 seconds delay to avoid whois server rejecting the query. This script checks to see if a domain has expired. It can be run in interactive and batch mode and provides facilities to alarm if a domain is about to expire in advance.

Ubuntu Linux configure Viewsonic VG1930WM 19" widescreen LCD for 1440×900 resolution

Posted on in Categories Debian Linux, Howto, Linux desktop, Linux distribution, Tip of the day, Tips, Troubleshooting, Tuning, Ubuntu Linux last updated May 21, 2007

As I said earlier you need to tweak few things to run this monitor with Intel 810 or 845 based chip-set under Ubuntu Linux.

In order to use higher resolution install updated Intel i8xx, i9xx display driver. It is provided by a package called xserver-xorg-video-intel. This package provides the driver for the Intel i8xx and i9xx family of chipsets, including i810, i815, i830, i845, i855, i865, i915, and i945 series chips.

Replace driver by running the apt-get command. Open your terminal and type command:
$ sudo apt-get install xserver-xorg-video-intel

Now run ddcprobe command to get monitor VertRefresh values and HorizSync rate:
$ sudo ddcprobe | grep monitorrange

monitorrange: 24-82, 50-75

24-82 is your HorizSync rates and the second pair is your VertRefresh (50-75) values.

Next reconfigure xserver ( video and monitor using auto detect feature:
$ sudo dpkg-reconfigure xserver-xorg

Set monitor resolution 1440 x 900 and others as per your requirement. Save the changes and reboot the system.

After login you can adjust screen resolution by visiting System > Preferences > Screen Resolution > Select desired screen resolution such as 1440 x 900 and save the changes.