Although fork() theoretically copies the address space of the parentprocess to create the child's address space, Unix normally does notactually make a real copy. Instead it marks everything as copy onwrite and then waits foreither the parent or the child to dirty a page, whereupon it does copiesonly as much as it has to. This makes forks much faster, which is veryimportant since things in Unix fork a lot.

(Disclaimer: this is the traditional implementation for paged virtualmemory. I don

One of the interesting challenges in writing shell scripts isfiguring out how to do as much as is practical with shell builtinsand primitives. Since Bourne shell builtins are such a limited andconstrained environment, the results can be somewhat perverse andpeculiar and thus neat and amusing.

(If you can find an efficient way of doing things, using builtins ismuch faster than having to resort to external programs, especially whenthe system is loaded.)

My challenge today was checking whether a word was in a list of words(

The fork() system call presents a problem for strict virtual memoryovercommit . Because it duplicates a process's virtualaddress space, strictly correct accounting requires that the childprocess be instantly charged for however much committed address space theparent process has; if this puts the system over the commit limit, the fork() should fail.

At the same time, in practice most fork() child processes don't usevery much of the memory that they're being charged for; almost all thetime they