LinuxWebLog.com

Extract IP address

sandip — Tue, 15 May 2012 20:22:24 +0000

One liner with grep to extract the IP addresses from a file.

grep -Eo '([0-9]{1,3}\.){3}[0-9]{1,3}' /path/to/file

The "-o" option prints only the matched parts.

One liner with perl:

perl -ne 'print if s/.*((\d{1,3}\.){3}\d{1,3}).*/\1/' /path/to/file

Find size of ext3 Journal

sandip — Fri, 13 Apr 2012 20:01:04 +0000

The journal is located at inode:

# tune2fs -l /dev/sda1 | awk '/Journal inode/ {print $3}'

The size of journal in Bytes is:

# debugfs -R "stat <inodenumber>" /dev/sda1 | awk '/Size: /{print $6}'|head -1

Note: "<>" is necessary around the inode number.

group writable web folders with setgid and ACL

sandip — Tue, 03 Apr 2012 15:18:54 +0000

Often times, there is need for web-accessible folders to be set up so all web-developers have write access.

Along with setgid option, ACL can be used so anyone in the group "web-developers"
would have write privileges to anything under web-accessible document root.

So unless the acl privileges is revoked specifically, it would just continue to work.

To enable ACL, add "acl" option to /etc/fstab file for the corresponding partition and remount.

Edit /etc/fstab:

/dev/mapper/home /home           ext4    defaults,acl        0       2

Remount:

# mount -o remount /home

Here is the commands to be used for the setup:

# groupadd developers
# chgrp -R developers /path/to/docroot
# find /path/to/docroot -type d -exec chmod g+s {} \;
# find /path/to/docroot -type d -exec setfacl -m g:developers:rwx,d:g:developers:rwx {} \;
# find /path/to/docroot -type f -exec setfacl -m g:developers:rw {} \;

Now anyone needing write access can be put in the "developers" group.

# usermod -G developers {username}

If you need the webserver to have write access to certain folders, then chown the location to be owned by the webserver, instead of giving write permissions to all.

# chown apache /path/to/docroot/apache

Getting the most out of Grub

sandip — Tue, 03 Apr 2012 12:40:53 +0000

The grub bootloader is particularly useful, especially when upgrading and testing new kernels. I recently found a way to modifiy the default boot config to make it useful when you wish to remotely upgrade a kernel and boot into it once only without being at the console to change the default back.

Original news source

munin-node mysql setup

sandip — Wed, 28 Mar 2012 18:33:23 +0000

munin-node installed via epel repository.
Install perl-Cache-Cache:

# yum install munin-node perl-Cache-Cache
Create file "/etc/munin/plugin-conf.d/mysql" with below contents:

[mysql*] env.mysqluser munin env.mysqlpassword {PASS}
Create mysql user and assign corresponding privileges:

mysql> create user munin@localhost identified by '{PASS}'; mysql> GRANT PROCESS, SUPER ON *.* TO 'munin'@'localhost'; mysql> GRANT SELECT ON `mysql`.* TO 'munin'@'localhost'; mysql> flush privileges
Check the suggestions and install the plugins:

munin-node-configure --suggest 2>/dev/null |grep mysql munin-node-configure --shell | grep mysql | sh
Test via:

# cd /etc/munin/plugins # munin-run mysql_connections

How to install oracle java 7 in ubuntu 12.04

david23 — Tue, 27 Mar 2012 14:31:52 +0000

Java is a programming language and computing platform first released by Sun Microsystems in 1995. It is the underlying technology that powers state-of-the-art programs including utilities, games, and business applications. Java runs on more than 850 million personal computers worldwide, and on billions of devices worldwide, including mobile and TV devices.

Original news source

Plesk courier-imap imapd on port 143 fails

sandip — Fri, 17 Feb 2012 01:53:35 +0000

After Plesk upgrade to 9.5.4, imapd on port 143 did not come up.

On checking the maillog, it was complaining about:

imapd: Invalid -maxprocsarg option.
imapd-ssl: Invalid -maxprocsarg option.

I noticed /etc/courier-imap/imapd had both the below lines commented:

#MAXDAEMONS=40
#MAXPERIP=4

Once I uncommented those values, I was able to get the imap listener up upon a `service courier-imap restart`.

Django postgresql connect_timeout via environment variable

sandip — Tue, 07 Feb 2012 04:03:57 +0000

Recently, I've had to move a postgresql database onto a separate server and split it out from the django application server.

On doing so, we saw intermittent "OperationalError: could not connect to server: Connection timed out".

This was quite obvious that the "connect_timeout" had to be increased to resolve the issue due to the latency introduced by the network. However, psycopg2 database adapter was being used which did not support the "connect_timeout" option to be passed via django.

We were able to work around the issue setting the environmental variable "PGCONNECT_TIMEOUT" so libpq would pick up the connection parameter.

Put the below in "django.wsgi":

os.environ['PGCONNECT_TIMEOUT'] = '30'

munin-node and postgresql plugins setup

sandip — Mon, 06 Feb 2012 00:37:31 +0000

While setting up munin to monitor postgresql, I was getting "[DBD::Pg not found, and cannot do psql yet]" when running `munin-node-configure --suggest | grep postgres`.

I confirmed that the rpm package "perl-DBI-1.52-2.el5" was indeed installed.

However, when I ran a test against the module, it failed with:

# perl -MDBD::Pg -e 1
Can't load '/usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi/auto/DBD/Pg/Pg.so' for module DBD::Pg: libpq.so.4: cannot open shared object file: No such file or directory at /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/DynaLoader.pm line 230.
 at -e line 0
Compilation failed in require.
BEGIN failed--compilation aborted.

On checking the library, it returned with "libpq.so.4 => not found":

# ldd /usr/lib64/perl5/vendor_perl/5.8.8/x86_64-linux-thread-multi/auto/DBD/Pg/Pg.so
	linux-vdso.so.1 =>  (0x00007fffb60bb000)
	libpq.so.4 => not found
	libc.so.6 => /lib64/libc.so.6 (0x00007fa36d2c2000)
	/lib64/ld-linux-x86-64.so.2 (0x00007fa36d845000)

Indeed libpq.so.4 was missing since postgresql90-libs was installed which only includes "libpq.so.5".

To get libpq.so.4, "compat-postgresql-libs" package needed to be installed.

Once installed the perl module test passed and I was able to get the munin plugins linked using:

# munin-node-configure --shell | grep postgres | sh

Configuring Bind RNDC

sandip — Wed, 28 Dec 2011 03:00:27 +0000

RNDC is a useful mechanism for administering DNS servers. If it is not configured, BIND complains about it.

Determine the locations where RNDC expects to find the config files.

# rndc status 
  rndc: neither /etc/rndc.conf nor /etc/rndc.key was found

Create the rndc config file:

# rndc-confgen > /etc/rndc.conf

Thy rndc conf file should also have the contents that need to go to "/etc/named.conf". See sample below:

# Use with the following in named.conf, adjusting the allow list as needed:
# key "rndc-key" {
# 	algorithm hmac-md5;
# 	secret "aitNuyDz9NkSZ0MbxeQKcQ==";
# };
# 
# controls {
# 	inet 127.0.0.1 port 953
# 		allow { 127.0.0.1; } keys { "rndc-key"; };
# };

Once the key and control section has been added to named.conf, restart named and test again with:

# rndc status