Create Desktop Environment in Suse Linux on AWS

Having a Desktop environment on a Cloud Instance is helpful in many ways. You can troubleshoot application connectivity, take proper HAR files and so on. Even having a desktop is cool!

Here is how you can install GNOME on any SUSE Linux instances in any Cloud Environments. Remember, once you install GNOME (or KDE or any desktop environment as a matter of fact), you need to use VNC to connect to it.

The same steps can be used on any Cloud environments like Oracle Cloud (OCI), AWS, Azure, GCP and so on.

 

Requirements:

- SSH client that allows X11 forwarding

- TightVNC Server and Client

* Here are the steps I took to install GNOME desktop:

1. ssh into the instance with root username

2. type 'yast2' to get into YaST2 Control Center

3. Select "Software" on the left side bar, select "Online Update" on the right side bar, and then hint Enter key. This step is to update the repository of the system

4. Select "Software" on the left side bar, select "software Management" on the right side bar, and then hint Enter key.

5. In the "Search Phrase" textbox in the Filter Search session, type "gnome", and then hint Enter key

6. Install everything that listed on the right side bar, if the error page about "Package Dependencies"pops up, select the first option under "possible solutions", and then click "OK -- Try Again"

7. Select "Accept" on the bottom right of the page, hint Enter key. It will install all the packages you selected.

8. After installing the packages, click "F9" key twice to exit out YaST2 Control Center

Here are the steps to install and configure VNCServer:

1. Open TCP port 5901 in the security group that the instance belongs.

2. In the instance, type "zypper install vnc"

3. After installing VNCServer, type "vncpasswd" to set the access password

4. type "vncserver :1" to start a vnc session

5. sudo vim /root/.vnc/xstartup

6. comment out the "twm &" by typing # in front of the phrase, and then add "/usr/bin/gnome &" to the next line

7. save and exit out the xstartup file

8. type "vncserver -kill :1"

9. type "vncserver :1" to start a new session to load the modified xstartup file

10. In your local host, download and install tightvnc: http://www.tightvnc.com/download.php

11. Open "TightVNC Viewer"

12. For the Remote Host, type your DNS for the instance, and then add "::5901" at the end of the line

13. Click "Connect"

14. Type your password you set by vncpasswd

15. Now you can access to your instance via VNC connection

 

Hope this helps.

 

Disk Metadata : Superblock, Directory and Inodes

Metadata

Filesystem blocks are user for 2 purposes : To store User data and Metadata

• User data - stores actual data contained in files
• Metadata - stores file system structural information such as superblock, inodes, directories

Metadata describes the structure of the file system. Most common metadata structure are superblock, inode and directories.

Superblocks

Every FS has a superblock which contains info about filesystems such as :

• File system type
• Size
• Status
• Information about other metadata structures
• • For filesystems with 1k blocksizes, a backup superblock can be found at block 8193
  • For filesystems with 2k blocksizes, at block 16384
  • For 4k blocksizes, at block 32768.

List backup superblocks:

# dumpe2fs /dev/hda3 | grep -i superblock

If Superblock  is corrupted, restore with backup :

# e2fsck -f -b 8193 /dev/sda3

 

Inode

 

 An inode is a data structure on a Linux Unix FS which stores stores basic information about a regular file, directory, or other file system objects.  

Recover deleted files used by any process in Linux from RAM memory.

Every thing in Linux is a File. A file in turn is actually a pointer to inode which contain the actual data on the disk, permissions, ownership. Now what happens when a file is deleted ? Only the link is removed by not the inode or the actual data. if a process is using the file, or if the file is open , the inode is not released for overwriting util the process is done with the file. Such files will remain in the server memory (RAM). 

Lets discuss how to recover such deleted files which is being used by a process.

Lets do it with an example.

Create a test file.
# touch testfile.txt

Echo some random data on it.
# cat /dev/random > testfile.txt

Open the file using some command like below.
# less  testfile.txt

# ps -ef | grep -i less

less 4607 root  4r  REG 254,4   21  
           8880214 /root/testing.txt (deleted)

All the open files remain in the memory and hence in the /proc filesystem. The important columns in the above output are the second one, which gives you the PID of the process that has the file open (4607), and the fourth one, which gives you the file descriptor (4). Now, we go look in /proc, where there will still be a reference to the inode, from which you can copy the file back.

# ls -l /proc/4607/fd/4
lr-x------ 1 root root 64 Apr  7 03:19 
             /proc/4607/fd/4 -> /root/testing.txt (deleted)

To recover the deleted file in memory, just copy as below.
 #cp /proc/4607/fd/4 testing.txt.bk


Hurray you got your file back. Just make sure not to use "-a" switch while copying the file as this will copy the broken softlink.

JK

 

Sendmail Error : NOQUEUE: SYSERR(root): No local mailer defined NOQUEUE: SYSERR(root): QueueDirectory (Q) option must be set

Error using m4 macro while building sendmail.cf from sendmail.mc on RHEL 6 / CentOS 6 flavors?

[root@cent1]# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

m4:/etc/mail/sendmail.mc:10: cannot open `/usr/share/sendmail-cf/m4/cf.m4': No such file or directory

[root@cent1]#

The above error is because the package sendmail-cf is not installed.

You will have the below error messages on the /var/log/maillog file also. 

sendmail[3215]: gethostbyaddr(10.0.3.15) failed: 2

sendmail[3215]: NOQUEUE: SYSERR(root): No local mailer defined

sendmail[3215]: NOQUEUE: SYSERR(root): QueueDirectory (Q) option must be set

The above error is because the sendmail.cf is not configured properly. 

Fix is to install the package sendmail-cf, build sendmail.cf from sendmail.mc and restart sendmail service.

Install the sendmail-cf

# yum install -y sendmail-cf

Comment the entry which makes the sendmail listens only to loopback address as below by adding "dnl" on /etc/mail/sendmail.mc

# vi /etc/mail/sendmail.mc

dnl # DAEMON_OPTIONS(`Port=smtp,Addr=127.0.0.1, Name=MTA')dnl

# m4 /etc/mail/sendmail.mc > /etc/mail/sendmail.cf

# service sendmail restart

Check if sendmail is started properly.

[root@cent1 ~]# netstat -tulnp |  grep -i :25

tcp        0      0 0.0.0.0:25                  0.0.0.0:*                   LISTEN      3748/sendmail

[root@cent1 ~]#

Hope this helps.

Jk

Set Setuid, Setgid and Sticky bit in Linux

Special permissions on files and directories in linux are : SetUID, SetGID and Sticky bit.

With the help of “chmod” command  we can implement the special permissions on file and directories.

SUID / Set User ID : A program is executed with the file owner's permissions (rather than with the permissions of the user who executes it).

SGID / Set Group ID : Files created in the directory inherit its GID, i.e When a directory is shared between the users , and sgid is implemented on that shared directory , when these users creates  directory, then the created directory has the same gid or group owner of its parent directory.

Sticky Bit :  It is used mainly used on folders in order to avoid deletion of a folder and its content by other user though he/she is having write permissions. If Sticky bit is enabled on a folder, the folder is deleted by only owner of the folder and super user(root). This is a security measure to suppress deletion of critical folders where it is having full permissions by others.

Grub Re-install for SUSE Linux

The below steps can be used to fix un-bootable SUSE Linux OS due to Grub corruption or any damage to GRUB boot loader.

Boot to the SLED or SLES 11 DVD (the SP1 DVD is also fine), select "Rescue System" and login as root.  At the command line enter "grub" and follow this example:

******************
linux:~ # grub

    GNU GRUB  version 0.97  (640K lower / 3072K upper memory)
 [ Minimal BASH-like line editing is supported.  For the first word, TAB
   lists possible command completions.  Anywhere else TAB lists the possible
   completions of a device/filename. ]

grub> find /boot/grub/stage1
 (hd0,0)

grub> root (hd0,0)
 Filesystem type is reiserfs, partition type 0xfd

grub> setup (hd0)
 Checking if "/boot/grub/stage1" exists... yes
 Checking if "/boot/grub/stage2" exists... yes
 Checking if "/boot/grub/reiserfs_stage1_5" exists... yes
 Running "embed /boot/grub/reiserfs_stage1_5 (hd0)"...  18 sectors are embedded.
succeeded
 Running "install /boot/grub/stage1 (hd0) (hd0)1+18 p (hd0,0)/boot/grub/stage2 /boot/
grub/menu.lst"... succeeded
Done.

grub> quit
******************

In this example the root partition is (hd0,0) as returned by the "find /boot/grub/stage1" command.  Use the correct root partition for your system as indicated by this command for the two commands that follow the first one.

Reboot the system and GRUB should come up appropriately.

This Doc is for SUSE Linux Enterprise Server 11 or SUSE Linux Enterprise Desktop 11 but it should work for all SLES and OpenSUSE editons with little and obvious modifications.