Close Putty sessions without exit confirmation dialog

January 14th, 2015

You can set this in Putty "Change Settings" -> "Window" -> "Behaviour", and uncheck "Warn before closing window". Save the config in "Session", and now all windows can be closed without any exit confirmation dialog.


Categories: Misc Tags:

resolved – su: cannot set user id: Resource temporarily unavailable

January 12th, 2015

When i try to log on as user "test", error occurred:

su: cannot set user id: Resource temporarily unavailable

I had a check of limits.conf:

[root@testvm ~]# cat /etc/security/limits.conf|egrep -v '^$|^#'
oracle   soft   nofile    131072
oracle   hard   nofile    131072
oracle   soft   nproc    131072
oracle   hard   nproc    131072
oracle   soft   core    unlimited
oracle   hard   core    unlimited
oracle   soft   memlock    50000000
oracle   hard   memlock    50000000
@svrtech    soft    memlock         500000
@svrtech    hard    memlock         500000
*   soft   nofile    131072
*   hard   nofile    131072
*   soft   nproc    131072
*   hard   nproc    131072
*   soft   core    unlimited
*   hard   core    unlimited
*   soft   memlock    50000000
*   hard   memlock    50000000

Then I had a check of the number of processes/threads with the maximum number of processes to see whether it's coming over the line:

[root@c9qa131-slcn03vmf0293 ~]# ps -eLF | grep test | wc -l

So it's not exceeding. Then I had a check of open files:

[root@testvm ~]# lsof | grep aime | wc -l


It's not exceeding 131072 either, then why the error "su: cannot set user id: Resource temporarily unavailable" was there? Actually the culprit was in file /etc/security/limits.d/90-nproc.conf:

[root@testvm ~]# cat /etc/security/limits.d/90-nproc.conf
# Default limit for number of user's processes to prevent
# accidental fork bombs.
# See rhbz #432903 for reasoning.

* soft nproc 1024
root soft nproc unlimited

After I modified 1024 to 131072, the issue gone away immediately.

Categories: IT Architecture, Kernel, Linux, Systems, Unix Tags:

resolved – Error: Unable to connect to xend: Connection reset by peer. Is xend running?

January 7th, 2015

Today I met some issue when trying to run xm commands on a XEN server:

[root@xenhost1 ~]# xm list
Error: Unable to connect to xend: Connection reset by peer. Is xend running?

I had a check, and found xend was actually running:

[root@xenhost1 ~]# /etc/init.d/xend status
xend daemon running (pid 8329)

After some debugging, I found it's caused by libvirtd & xend corrupted. And then I did a bounce of them:

[root@xenhost1 ~]# /etc/init.d/libvirtd restart
Stopping libvirtd daemon: [ OK ]
Starting libvirtd daemon: [ OK ]

[root@xenhost1 ~]# /etc/init.d/xend restart #this may not be needed 
restarting xend...
xend daemon running (pid 19684)

Later, the xm commands went good.


For more information about libvirt, you can check here.


Categories: Clouding, IT Architecture, Oracle Cloud Tags:

remove entries in perl array with specified value

December 30th, 2014

Assume that in array @array_filtered:

my @array_filtered = ("your", "array", "here", 1, 3, 8, "here", 2, 5, 9, "sit", "here",3, 4, 7,"yes","now",8,1,7,6); #or my @array_filtered=qw(your array here 1 3 8 here 2 5 9 sit here 3 4 7 yes now 8 1 7 6) which uses Alternative Quotes(q, qq, qw, qx)

You want to remove entries that have value "here" or "now" and it's following 3 entries, you can use splice:

my @array_filtered = ("your", "array", "here", 1, 3, 8, "here", 2, 5, 9, "sit", "here",3, 4, 7,"yes","now",8,1,7,6);
my @search_for = ("here","now");
#return keys that have specified value, =~/!~ for regular expression, eq/ne for string, ==/!= for number. or use unless()/if(not()). use m{} instead of // if there's too much / in the expression and you're tired of using \/ to escape them.

@index_all = grep { $array_filtered[$_] =~ /$search_for_s/ } 0..$#array_filtered;

for($i=0;$i<=$#index_all;$i++) {
@index_all_one = grep { $array_filtered[$_] =~ /$search_for_s/ } 0..$#array_filtered;
#print $indexone."\n"

print "@array_filtered"."\n";

The output is "your array sit yes 6".


  • For more info about perl regular expression(such as operators<m, s, tr> and their modifiers, complex regular expression cheat sheet<.\s\S\d\D\w\W[aeiou][^aeiou](foo|bar), \G, $, $&, $`, $'> and more), you can refer to this article.
  • The following is about perl alternative quotes:

q// is generally the same thing as using single quotes - meaning it doesn't interpolate values inside the delimiters.
qq// is the same as double quoting a string. It interpolates.
qw// return a list of white space delimited words. @q = qw/this is a test/ is functionally the same as @q = ('this', 'is', 'a', 'test')
qx// is the same thing as using the backtick operators.

Categories: IT Architecture, Perl, Programming Tags:

resolved – cssh installation on linux server

December 29th, 2014

ClusterSSH can be used if you need controls a number of xterm windows via a single graphical console window, and you want to run commands interactively on multiple servers over an ssh connection. This guide will show the process to install clusterssh on a linux box from tarball.

At the very first, you should download cssh tarball App-ClusterSSH-4.03_04.tar.gz from sourceforge. You may need export proxy settings if it's needed in your env:

export https_proxy=
export http_proxy=
export ftp_proxy=

After the proxy setting, you can now get the package:

wget ''
tar zxvf App-ClusterSSH-4.03_04.tar.gz
cd App-ClusterSSH-4.03_04

Before installing, let's install some prerequisites packages:

yum install gcc libX11-devel gnome* -y
yum groupinstall "X Window System" -y
yum groupinstall "GNOME Desktop Environment" -y
yum groupinstall "Graphical Internet" -y
yum groupinstall "Graphics" -y

Now run "perl Build.PL" as indicated by README:

[root@centos-32bits App-ClusterSSH-4.03_04]# perl Build.PL
Can't locate Module/ in @INC (@INC contains: /usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/site_perl/5.8.8 /usr/lib/perl5/site_perl /usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi /usr/lib/perl5/vendor_perl/5.8.8 /usr/lib/perl5/vendor_perl /usr/lib/perl5/5.8.8/i386-linux-thread-multi /usr/lib/perl5/5.8.8 .) at Build.PL line 5.
BEGIN failed--compilation aborted at Build.PL line 5.

As it challenged, you need install first. Let's use cpan to install that module.

Run "cpan" and enter "follow" when below info occurred:

Policy on building prerequisites (follow, ask or ignore)? [ask] follow

If you had already ran cpan before, then you can configure the policy as below:

cpan> o conf prerequisites_policy follow
cpan> o conf commit

Now Let's install Module::Build:

cpan> install Module::Build

After the installation, let's run "perl Build.PL" again:

[root@centos-32bits App-ClusterSSH-4.03_04]# perl Build.PL
Checking prerequisites...
    !  Exception::Class is not installed
    !  Tk is not installed
    !  Try::Tiny is not installed
    !  X11::Protocol is not installed
    !  CPAN::Changes is not installed
    !  File::Slurp is not installed
    !  File::Which is not installed
    !  Readonly is not installed
    !  Test::Differences is not installed
    !  Test::DistManifest is not installed
    !  Test::PerlTidy is not installed
    !  Test::Pod is not installed
    !  Test::Pod::Coverage is not installed
    !  Test::Trap is not installed

ERRORS/WARNINGS FOUND IN PREREQUISITES.  You may wish to install the versions
of the modules indicated above before proceeding with this installation

Run 'Build installdeps' to install missing prerequisites.

Created MYMETA.yml and MYMETA.json
Creating new 'Build' script for 'App-ClusterSSH' version '4.03_04'

As the output says, run "./Build installdeps" to install the missing packages. Make sure you're in GUI env(through vncserver maybe), as "perl Build.PL" has a step to test GUI.

[root@centos-32bits App-ClusterSSH-4.03_04]# ./Build installdeps


Running Mkbootstrap for Tk::Xlib ()
chmod 644 ""
"/usr/bin/perl" "/usr/lib/perl5/5.8.8/ExtUtils/xsubpp" -typemap "/usr/lib/perl5/5.8.8/ExtUtils/typemap" -typemap "/root/.cpan/build/Tk-804.032/Tk/typemap" Xlib.xs > Xlib.xsc && mv Xlib.xsc Xlib.c
make[1]: *** No rule to make target `pTk/tkInt.h', needed by `Xlib.o'. Stop.
make[1]: Leaving directory `/root/.cpan/build/Tk-804.032/Xlib'
make: *** [subdirs] Error 2
/usr/bin/make -- NOT OK
Running make test
Can't test without successful make
Running make install
make had returned bad status, install seems impossible

Errors again, we can see it's complaining something about TK related thing. To resolve this, I manully installed the latest perl-tk module as below:

wget --no-check-certificate ''
unzip master
cd perl-tk-master
perl Makefile.PL
make install

After this, let's run "./Build installdeps" and "perl Build.PL" again which all went through good:

[root@centos-32bits App-ClusterSSH-4.03_04]# ./Build installdeps

[root@centos-32bits App-ClusterSSH-4.03_04]# perl Build.PL

And let's run ./Build now:

[root@centos-32bits App-ClusterSSH-4.03_04]# ./Build
Building App-ClusterSSH
Generating: ccon
Generating: crsh
Generating: cssh
Generating: ctel

And now "./Build install" which is the last step:

[root@centos-32bits App-ClusterSSH-4.03_04]# ./Build install

After installation, let's have a test:

[root@centos-32bits App-ClusterSSH-4.03_04]# echo 'svr testserver1 testserver2' > /etc/clusters

Now run 'cssh svr', and you'll get the charm!



Categories: Clouding, IT Architecture, Linux, Systems, Unix Tags:

resolved – error:0D0C50A1:asn1 encoding routines:ASN1_item_verify:unknown message digest algorithm

December 17th, 2014

Today when I tried using curl to get url info, error occurred like below:

[root@centos-doxer ~]# curl -i --user username:password -H "Content-Type: application/json" -X POST --data @/u01/shared/addcredential.json -v

* About to connect() to port 443

*   Trying connected

* Connected to ( port 443

* successfully set certificate verify locations:

*   CAfile: /etc/pki/tls/certs/ca-bundle.crt

  CApath: none

* SSLv2, Client hello (1):

SSLv3, TLS handshake, Server hello (2):

SSLv3, TLS handshake, CERT (11):

SSLv3, TLS alert, Server hello (2):

error:0D0C50A1:asn1 encoding routines:ASN1_item_verify:unknown message digest algorithm

* Closing connection #0

After some searching, I found that it's caused by the current version of openssl(openssl-0.9.8e) does not support SHA256 Signature Algorithm. To resolve this, there are two ways:

1. add -k parameter to curl to ignore the SSL error

2. upgrade openssl to at least openssl-0.9.8o. Here's the way to upgrade openssl:

wget --no-check-certificate ''
tar zxvf openssl-0.9.8o.tar.gz
cd openssl-0.9.8o
./config --prefix=/usr --openssldir=/usr/openssl
make test
make install

After this, run openssl version to confirm:

[root@centos-doxer openssl-0.9.8o]# /usr/bin/openssl version
OpenSSL 0.9.8o 01 Jun 2010


If you installed openssl from rpm package, then you'll find the openssl version is still the old one even after you install the new package. This is expected so don't rely too much on rpm:

[root@centos-doxer openssl-0.9.8o]# /usr/bin/openssl version
OpenSSL 0.9.8o 01 Jun 2010

Even after rebuilding rpm DB(rpm --rebuilddb), it's still the old version:

[root@centos-doxer openssl-0.9.8o]# rpm -qf /usr/bin/openssl

[root@centos-doxer openssl-0.9.8o]# rpm -qa|grep openssl