avoid putty ssh connection sever or disconnect

January 17th, 2014

After sometime, ssh will disconnect itself. If you want to avoid this, you can try run the following command:

while [ 1 ];do echo hi;sleep 60;done &

This will print message "hi" every 60 seconds on the standard output.

PS:

You can also set some parameters in /etc/ssh/sshd_config, you can refer to http://www.doxer.org/make-ssh-on-linux-not-to-disconnect-after-some-certain-time/

“Include snapshots” made NFS shares from ZFS appliance shrinking

January 17th, 2014

Today I met one weird issue when checking one NFS share mounted from ZFS appliance. The NFS filesystem mounted on client was shrinking when I removed files as the space on that filesystem was getting low. But what made me confused was that the filesystem's size would getting lower! Shouldn't the free space getting larger and the size keep unchanged?

After some debugging, I found that this was caused by ZFS appliance shares' "Include snapshots". When I uncheck "Include snapshots", the issue was gone!

zfs-appliance

Categories: Hardware, NAS, Storage Tags:

resolved – ESXi Failed to lock the file

January 13th, 2014

When I was power on one VM in ESXi, one error occurred:

An error was received from the ESX host while powering on VM doxer-test.
Cannot open the disk '/vmfs/volumes/4726d591-9c3bdf6c/doxer-test/doxer-test_1.vmdk' or one of the snapshot disks it depends on.
Failed to lock the file

And also:

unable to access file since it is locked

This apparently was caused by some storage issue. I firstly googled and found most of the posts were telling stories about ESXi working mechanism, and I tried some of them but with no luck.

Then I thought of that our storage datastore was using NFS/ZFS, and NFS has file lock issue as you know. So I mount the nfs share which datastore was using and removed one file named lck-c30d000000000000. After this, the VM booted up successfully! (or we can log on ESXi host, and remove lock file there also)

install java jdk on linux

January 7th, 2014

Here's the steps if you want to install java on linux:

wget <path to jre-7u25-linux-x64.rpm> -P /tmp
rpm -ivh /tmp/jre-7u25-linux-x64.rpm
mkdir -p /root/.mozilla/plugins
rm -f /root/.mozilla/plugins/libnpjp2.so
ln -s /usr/java/jre1.7.0_25/lib/amd64/libnpjp2.so /root/.mozilla/plugins/libnpjp2.so
ll /root/.mozilla/plugins/libnpjp2.so

PS:

  • You'll need to install jre i386 version if your firefox browser is 32 bits. And you can install jre6 from here. You should download packages like "jre-6u33-linux-i586-rpm.bin" and run chmod +x jre-6u33-linux-i586-rpm.bin && ./jre-6u33-linux-i586-rpm.bin after that. You may locate /usr/java/jre1.6.0_33/bin/javaws for opening remote console when prompted.
  • If you want to install java plugin of firefox on linux, or even install firefox under linux, then you can refer to this article.

add another root user and set password

January 7th, 2014

In linux, do the following to add another root user and set password:

mkdir -p /home/root2
useradd -u 0 -o -g root -G root -s /bin/bash -d /home/root2 root2
echo password | passwd --stdin root2

Categories: IT Architecture, Linux, Systems Tags:

self defined timeout for telnet on Linux

December 26th, 2013

telnet's default timeout value is relative high, so you may want to change timeout value to lower value such as 5 seconds. Here's the way that we can fulfill this:

#!/bin/bash

timeout()
{
waitfor=5
command=$*
$command &
commandpid=$!
( sleep $waitfor ; kill -9 $commandpid > /dev/null 2>&1 ) &
watchdog=$!
sleeppid=$PPID
wait $commandpid > /dev/null 2>&1
kill $sleeppid > /dev/null 2>&1
}

timeout telnet slcc29-scan1.us.oracle.com 1521 >> $output

Also, we can use expect and set timeout for expect. When telnet is integrated with expect, we can fulfill timeout for telnet through using expect's timeout value:

#!/usr/bin/expect

set timeout 30

send "<put telnet command here>\r"

Add static routes in linux which will survive reboot and network bouncing

December 24th, 2013

We can see that in linux, the file /etc/sysconfig/static-routes is revoked by /etc/init.d/network:

[root@test-linux ~]# grep static-routes /etc/init.d/network
# Add non interface-specific static-routes.
if [ -f /etc/sysconfig/static-routes ]; then
grep "^any" /etc/sysconfig/static-routes | while read ignore args ; do

So we can add rules in /etc/sysconfig/static-routes to let network routes survive reboot and network bouncing. The format of /etc/sysconfig/static-routes is like:

any net 10.247.17.0 netmask 255.255.255.192 gw 10.247.10.1
any net 10.247.11.128 netmask 255.255.255.192 gw 10.247.10.1

To make route in effect immediately, you can use route add:

route add -net 192.168.62.0 netmask 255.255.255.0 gw 192.168.1.1

But remember that to change the default gateway, we need modify /etc/sysconfig/network(modify GATEWAY=).

After the modification, bounce the network using service network restart to make the changes in effect.

PS: 

  • You need make sure network id follows -net, or you'll see error "route: netmask doesn't match route address".
  • To reload all static routes in /etc/sysconfig/static-routes, you can do the following:
      # Add non interface-specific static-routes.
        if [ -f /etc/sysconfig/static-routes ]; then
           grep "^any" /etc/sysconfig/static-routes | while read ignore args ; do
              /sbin/route add -$args
           done
        fi

remove duplicate images using fdupes and expect in linux

December 13th, 2013

I've got several thousands of pictures, but most of them had several exact copies of themselves. So I had to remove duplicate ones by hand firstly.

Later, I thought of that in linux we had md5sum which will give the same string for files with exact same contents. Then I tried to write some program, and that toke me some while.

I searched google and found that in linux, we had fdupes which can do the job very well. fdupes will calculate duplicate files based on file size/md5 value, and will prompt you to reserve one copy or all copies of the duplicates and remove others if you gave -d parameter to it. You can read more about fdupes here http://linux.die.net/man/1/fdupes

As all the pictures were on a windows machine, so I installed cygwin and installed fdupes and expect. Later I wrote a small script to reserve only one copy of the duplicate pictures for me(you will have to enter your option either reserving one copy or all copies by hand if you do not use expect, as there's no option for reserve one copy by the author of fdupes). Here's my program:

$ cat fdupes.expect
#!/usr/bin/expect
set timeout 1000000
spawn /home/andy/fdupes.sh
expect "preserve files" {
send "1\r";exp_continue
}

$ cat /home/andy/fdupes.sh
fdupes.exe -d /cygdrive/d/pictures #yup, my pictures are all on this directory on windows, i.e. d:\pictures

After this, you can just run fdupes.expect, and it will reserve only one copy and remove other duplicates for you.

PS: Here's man page of fdupes https://github.com/adrianlopezroche/fdupes

Common storage multi path Path-Management Software

December 12th, 2013
Vendor Path-Management Software URL
Hewlett-Packard AutoPath, SecurePath www.hp.com
Microsoft MPIO www.microsoft.com
Hitachi Dynamic Link Manager www.hds.com
EMC PowerPath www.emc.com
IBM RDAC, MultiPath Driver www.ibm.com
Sun MPXIO www.sun.com
VERITAS Dynamic Multipathing (DMP) www.veritas.com

resolved – mount clntudp_create: RPC: Program not registered

December 2nd, 2013

When I did a showmount -e localhost, error occured:

[root@centos-doxer ~]# showmount -e localhost
mount clntudp_create: RPC: Program not registered

So I checked what RPC program number of showmount was using:

[root@centos-doxer ~]# grep showmount /etc/rpc
mountd 100005 mount showmount

As this indicated, we should startup mountd daemon to make showmount -e localhost work. And mountd is part of nfs, so I started up nfs:

[root@centos-doxer ~]# /etc/init.d/nfs start
Starting NFS services: [ OK ]
Starting NFS quotas: [ OK ]
Starting NFS daemon: [ OK ]
Starting NFS mountd: [ OK ]

Now as mountd was running, showmount -e localhost should work.