What is a Zombie Process
Zombie Process
On Unix operating systems, a zombie process or defunct process is a process that has completed execution but still has an entry in the process table, allowing the process that started it to read its exit status. The term zombie process derives from the common definition of zombie—an undead person. In the term's colorful metaphor, the child process has died but has not yet been reaped.
When a process ends, all of the memory and resources associated with it are deallocated so they can be used by other processes. However, the process's entry in the process table remains. The parent is sent a SIGCHLD signal indicating that a child has died; the handler for this signal will typically execute the wait system call, which reads the exit status and removes the zombie. The zombie's process ID and entry in the process table can then be reused. However, if a parent ignores the SIGCHLD, the zombie will be left in the process table. In some situations this may be desirable, for example if the parent creates another child process it ensures that it will not be allocated the same process ID.
A zombie process is not the same as an orphan process. Orphan processes don't become zombie processes; instead, they are adopted by init (process ID 1), which waits on its children.
Zombies can be identified in the output from the Unix ps command by the presence of a "Z" in the STAT column. Zombies that exist for more than a short period of time typically indicate a bug in the parent program. As with other leaks, the presence of a few zombies isn't worrisome in itself, but may indicate a problem that would grow serious under heavier loads.
To remove zombies from a system, the SIGCHLD signal can be sent to the parent manually, using the kill command. If the parent process still refuses to reap the zombie, the next step would be to remove the parent process. When a process loses its parent, init becomes its new parent. Init periodically executes the wait system call to reap any zombies with init as parent.
When a process ends, all of the memory and resources associated with it are deallocated so they can be used by other processes. However, the process's entry in the process table remains. The parent is sent a SIGCHLD signal indicating that a child has died; the handler for this signal will typically execute the wait system call, which reads the exit status and removes the zombie. The zombie's process ID and entry in the process table can then be reused. However, if a parent ignores the SIGCHLD, the zombie will be left in the process table. In some situations this may be desirable, for example if the parent creates another child process it ensures that it will not be allocated the same process ID.
A zombie process is not the same as an orphan process. Orphan processes don't become zombie processes; instead, they are adopted by init (process ID 1), which waits on its children.
Zombies can be identified in the output from the Unix ps command by the presence of a "Z" in the STAT column. Zombies that exist for more than a short period of time typically indicate a bug in the parent program. As with other leaks, the presence of a few zombies isn't worrisome in itself, but may indicate a problem that would grow serious under heavier loads.
To remove zombies from a system, the SIGCHLD signal can be sent to the parent manually, using the kill command. If the parent process still refuses to reap the zombie, the next step would be to remove the parent process. When a process loses its parent, init becomes its new parent. Init periodically executes the wait system call to reap any zombies with init as parent.
$ ps -aef -H (will list all processes with hierarchy structure.)
$ kill -9 5373 (Here 5343 is the process id)
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Moonwalk (dance)
Moonwalk
(Dance)
I am very fascinated by this moonwalk dance step. I really enjoy whenever I see someone doing a moonwalk step. The best moonwalker I have seen till date is Michael Jackson.
The moonwalk or backslide is a dance technique that presents the illusion of the dancer being pulled backwards while attempting to walk forward. A popping move, it became popular around the world after Michael Jackson executed the dance move during a performance of "Billie Jean" on Motown 25: Yesterday, Today, Forever on March 25, 1983. It subsequently became his signature move, and is now one of the best-known dance techniques in the world.
An illusion is involved in creating the appearance of the dancer gliding in backwards direction. Initially, the front foot is held flat on the ground, while the back foot is in a tiptoe position. The flat front foot remains on the ground but is slid lightly and smoothly backward past the tip-toe back foot. What is now the front foot is lowered flat, while the back foot is raised into the tiptoe position. These steps are repeated over and over. Variations of this move allow the backslider to also appear to glide forwards, sideways, and even in a circle.
An illusion is involved in creating the appearance of the dancer gliding in backwards direction. Initially, the front foot is held flat on the ground, while the back foot is in a tiptoe position. The flat front foot remains on the ground but is slid lightly and smoothly backward past the tip-toe back foot. What is now the front foot is lowered flat, while the back foot is raised into the tiptoe position. These steps are repeated over and over. Variations of this move allow the backslider to also appear to glide forwards, sideways, and even in a circle.
So if you wanna learn this moonwalk step, then follow the instruction..
MOONWALK
Watch this video[ MOONWALK ], I am sure you'll learn the technique.
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Generation Gap
The generation gap is a popular term used to describe differences between people of a younger generation and their elders, especially between a child and his or her parent's generation. The term first became popularized in Western countries during the 1960s and described the cultural differences between the young and their parents.
The generation gap is the accumulation of differences, subtleties, and ideas between people born during separate time periods. The gap often leads to misunderstanding and lack of trust between the two parties. The elders are more critical of the younger generation with a big inventory of complaints against the young and the young mostly tend to ignore the grumbling, mumbling and occasional loud protestations of the older generation. But now and then they do protest. They resent the petting attitude of the elders.
The generation gap is the constant struggle of the parents to prevent their kids from doing things that their own experiences and wisdom tell them is going to harm their kids. The kids on the other hand try constantly to prove to the parents that they are equipped to take control of their lives. Neither is wrong - they are both right in their own premise. The parents blinded by their love for the kids would rather have their own experiences replace the experiences of their kids. Whereas, the kids are convinced that their decisions are right and are based on current situations that the parents may not necessarily be aware of. Their most common statement is "Ma things are different now"
The most common mistake the parents make is that they do not treat kids their age - its either they are too young or they measure them at their own level.
There may be the following differences between the old and the young:
- Of ideas on general conduct comprising dress, food habits etc.
- Morality, marriage & career
- Of tastes on art, music, literature, and in short total outlook.
- Family unit breaking up and gradually losing the importance it once had. The central authority of the paternal figure becoming redundant.
- Imposition of the self-righteous attitude of the older generation on the young.
- Biological evolutionary difference
It's not necessary that the kids do not understand their parents' love and their concern but they just think that they are in a different era. Till such time people themselves do not become parents and get to the same pedestal they do not realize.
The generation gap is of course not a given for all families. There are many households where it doesn't occur at all. There are fights and arguments and children defying their parents but these are occasional and minor.
What then are these families doing right? Here are a few of their secrets: -
- Lots of communication and involvement - this one's obvious but not always easy to follow. It just means that if you're not talking to the children because you're too busy or too mad at them or because you disagree with whatever they say then you've cut off your channel of communication. So what you need to remember when dealing with teenagers is that they may be insufferable know alls a lot of the time but they'll learn that there are gray shades between the blacks and the whites soon enough. Also that intolerance or a judgemental attitude will hurt you more than your child.
- Lots of time spent together in play and fun- its harder to think you hate your mom or dad when you spend a large part of your week having fun with them. It's even harder when in many ways they are your best friends. Clear boundaries - thus far and no further or they will face clearly defined consequences. As long as children know this, you and they both can be much freer with each other without you worrying about being taken advantage of.
- Clear values - make it clear that everything has to be earned. If they want respect for their opinions they have to learn to respect the opinions of others. Similarly other values to stress are honesty, compassion and tolerance.
- Foster self-dependence - essentially this means teach them to know their own minds and make their own decisions. This will help them to keep their balance in the face of peer pressure. Self-dependence starts early - let your child have a say in family affairs as well as in matters personally affecting him from the time that he is a toddler. Let him help with family chores and earn a part of his own money. Make it clear that even when he makes mistakes, it's not the end of the world - it's an essential part of the learning process.
Generation gaps can be reduced to some extent by making efforts. I must mention here most efforts must come from the parents - they have the wisdom. It becomes easier to adjust if the parents constantly refresh their memories by their own past outrageousness.
Hope you enjoyed reading this blog post. Please input your valuable comment and share your personal experiences. ~Rohan Rawat
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How to add an account to the sudoer list
Add an account to the sudoer list
When logged in as a user with sudo privileges:
sudo adduser name_of_user admin
2) Graphical Interface
Go to System--> Administration --> Users and Groups.
Then:
(1) Click on the name of the user that you want to elevate.
(2) Click on the properties button to open a new settings window.
(3) In the new window, click on the User Priviledges tab.
(4) Check the box next to "Executing system administration tasks".
Click OK all the way out, and that user should now be able to sudo.
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How to Install NFS Server
NFS Server
The Network File System (NFS) was developed to allow machines to mount a disk partition on a remote machine as if it were a local disk. It allows for fast, seamless sharing of files across a network.
It also gives the potential for unwanted people to access your hard drive over the network (and thereby possibly read your email and delete all your files as well as break into your system) if you set it up incorrectly.$ sudo aptitude -P install nfs-kernel-server nfs-common portmap When configuring portmap do =not= bind loopback. If you do you can either edit /etc/default/portmap by hand or run:
$ sudo dpkg-reconfigure portmap If you have edited the file by hand you can restart portmap via:
$ sudo /etc/init.d/portmap restart Note: It is not necessary to install NFS on client machines which are not going to be sharing any of their own directories. Sharing Local Folders To specify a folder you will need to edit /etc/exports, which can be done like (replace vi for your favorite editor):
$ sudo vi /etc/exports For an example I will share, with full read/write and privileges, my share directory. This directory will be broadcasted to every local IP from 192.168.1.1 through 192.168.1.255.
$ /home/rohan/share 192.168.1.1/24(rw,no_root_squash,async)To share a read only drive, for example on a Windows NTFS drive, you can use something like the following:
/media/songs/music 192.168.1.1/24(ro,async)
$ sudo /etc/init.d/nfs-kernel-server restart After making changes to /etc/export you can make the shares effect by issuing the:
sudo exportfs -a *Use on the other PC - Last you will need to mount the volume on the other computer. So, ether shift screens or SSH to lab2 and open a terminal. You can only mount into another folder which must be created.
sudo mkdir ~/music Now mount music from lab1 into ~/music at lab2.
$ sudo mount 192.168.1.2:/media/songs/music ~/music
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