17
Oct/090

Linux: Remove installed RPM packages manually

Sometimes you screw up an application and are unable to use rpm -e to remove them from your system. Here is how you go about doing that:

To find installed RPM packages:

rpm -qa | grep <string>

To remove:

rpm -e --nodeps --allmatches <package name>
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12
Jul/090

Misc: Error 500 – Internal server error while editing posts – unable to view wordpress dashboard items

If it’s only happening to a few posts or you can’t see all items/boxes in your dashboard then it’s your php module starving for more memory.

If you’re hosting the site, edit php.ini and add give it more memory. If you don’t know where php.ini is use the following command:

find / -name "php.ini"

Find memory section and dedicate what you want.

If your site is hosted, then create a php.ini file in wp-admin directory, and add the following line:

memory=15MB

If 15 is not good enough try 20 or 30.

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6
Jul/093

Linux: vsftpd and symbolic links

vsftpd is all about security, and that’s why you cannot access linked directories through vsftpd with any ftp client. My arguement is that if you know how to use symlinks, or are careful enough not to link directories you don’t want to share then who’s vsftpd to butt in and completely disallow you to use such convenient feature of an OS? Reminds me of Windows Server type security… they block IE by default so that you have to either allow every single site, or disable IE ESC altogether.

Here is my convenient workaround: use mount bind!

mount --bind /sourcedirectory /destinationdirectory

You can either use @reboot cron job to have the directories mounted, or mount though fstab by adding the following line:

/directory-you-want-to-mount /destination-directory none bind

Haa… gotcha, but don’t go too fast! This is mount, not ln and will NOT create a mount point in your destination directory. For instance, if you want to mount /home/share to /home/user/share you will need to create /home/user/share first, then mount. Also keep in mind that if you have a copy or rsync job to copy contents of /home/share AND /home/user recursively, you will create two full copies of /home/share directory. One in /home/share and one in /home/user/share. Exclude one of the directories from your cp or rsync job.

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5
Jul/090

Linux: Share a directory between local users

I spent a few hours yesterday trying to get this done but ran into several problems, and worst of all, I couldn’t find one single post addressing all permission problems associated with allowing several users access to the same directory for read/write operations.

The best way of creating a shared directory is to create a user and group, and then a home directory. Make other users members of the new group and set permission inheritence to propagate to child objects regardless of the user who is creating or uploading the file.

User name is shareowner and group, sharedhome.

Create a user, group and home directory for the new user:

useradd -d /home/shareowner -g sharedhome -m shareowner

The above command creates a user and group as user’s primary group. I wouldn’t create a password for the user if I don’t want the user to actually be able to logon to the server. Once the home directory is created I will add the existing users to the new group:

usermod -G sharedhome existinguser1
usermod -G sharedhome existinguser2

and so on. Note that I use -G and not -g, as I want users to become additional users of the new group. Now we set permissions for the new directory… I make shareowner the owner, and sharedhome the group that owns the directory:

chown -R shareowner:sharedhome /home/sharedhome

Then I use umask and chmod to force all files in /home/sharedhome to inherit permissions from the top directory:

umask 002
chmod -R g+s /home/sharedhome

That’s it. Now existinguser1 and existinguser2 should have read/write permission to /home/sharedhome directory.

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22
Jun/090

Debian: open-iscsi, use iSCSI initiator to connect to a SAN

It is actually quite easy as long as your kernel is 2.6.16 or newer. Debian supports fibre channel out of the box, and for iSCSI you only need to install the open-iscsi package (you can easily taylor this to your distro):

aptitude install open-iscsi

Once the package is installed restart the initiator:

/etc/init.d/open-iscsi restart

To find out the indentifier name take a look at initiatorname.iscsi file:

cat /etc/iscsi/initiatorname.iscsi

You can find the initiator identifier towards the bottom of the file… mine is InitiatorName=iqn.1993-08.org.debian:01:61ddbbf82a70. Once you found the name you should be able to discover the target with the following command (my LeftHandNetworks iSCSI SAN IP is 192.168.1.70):

iscsiadm -m discovery -t sendtargets -p 192.168.1.70

Make a note of the record ID (mine is iqn.2003-10.com.lefthandnetworks:sancrp:3139:debian) and connect to it using the following command:

iscsiadm --mode node --targetname iqn.2003-10.com.lefthandnetworks:sancrp:3139:debian --portal 192.168.1.70:3260 --login

Once you initiated the command your iSCSI target will become visible to the OS as an SCSI disk (/dev/sda). You can now partition, format and then mount the LUN just like any other storage device. Add the target to your fstab and it should be auto-mounted everytime your system boots.

nano /etc/fstab

and add:

/dev/sda1   /iscsi   ext3   _netdev   0   0

To have the LUN mounted to /iscsi directory. It didn’t work that well in my case… fstab mounts devices early during startup and before iscsi init, and OS couldn’t find the target to mount. I ended up scripting the initiator and mount… created a file “initiscsi” in /etc/init.d directory and added the following lines:

iscsiadm --mode node --targetname iqn.2003-10.com.lefthandnetworks:sancrp:3139:debian --portal 192.168.1.70:3260 --login
sleep 5
mount -t ext3 /dev/sda1 /iscsi

I’m sure there is a proper way to have the session initiated before the mount, but I didn’t care enough to figure it out. Init and mount script will do just fine in my case since my LUN is just a storage device.

That sleep command is to make sure the LUN is visible to the OS before it’s mounted. I added the script to my startup sequence after making it executable:

chmod +x initiscsi
update-rc.d initiscsi defaults

This is of course for Debian startup.

If you are using CHAP you will need to edit your iscsid.conf file:

nano /etc/iscsi/iscsid.conf

and update it with correct authentication info:

node.startup = automatic
node.session.auth.username = username
node.session.auth.password = password
discovery.sendtargets.auth.username = username
discovery.sendtargets.auth.password = password

Save and close the file, then initiate discovery.

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