posborne / linux-programming-interface-exercises Goto Github PK

Hi there,
I'm learning from TLPI at the moment and in chapter 4. I was doing the cp exercise and I'm somewhat stuck. I saw your solution and implement it. However, the output isn't any different from the actual copy.c fiile. In both cases, the files are copying the holes. Also, in your code, you have the following line as well: while ((numRead = read(inputFd, buf, BUF_SIZE)) > 0), which says that the loop will continue unless there is an EOF - similar to the actual copy.c file as well. Can you tell me how your version of cp.c is any different from copy.c given that it is giving me identical output? The file I'm referring to is this one.
Thanks.

Hi!

I want before login with "rc.local" the command /bin/chattr +i or /bin/chattr +a /path/to/file

"rc.local"
#!/bin/sh
mount -t ramfs -o rw,size=1024M ramfs /path/to/folder
/bin/sleep 4

/bin/tar xvzf /path/to/file.tar.gz -C /path/to/folder
/bin/sleep 4

/bin/chattr +a /path/to/file
/bin/sleep 2

exit 0

chattr +a don't set the +a attribute. chattr can't set the attribute of the file, because
error message says the file is not there, but the file is there.

When I set it manually, then it works.

What's wrong?

I find it better to use code like this

        write(outputFd, buf, numRead);

'dup2' should not check the validation of 'newfd'.
close it directly and sliently.

Hello, your ideas have impressed and helped me a lot. Thanks!
Exercise 9-5 answer may have a mistake.

// setuid()
/* suspend not possible */
/* resume not possible */
setuid(getuid());  /* Permanently drop privileges*/

Hi, I have a few quick questions about your implementation for this exercise.

For your implementation of setenv:

I think that the function as written currently could potentially cause a memory leak and/or shrink the existing environment list. If an environment variable is already defined in the list, and it's found as you iterate through the list, the new value for the environment variable is set appropriately (assuming overwrite != 0). When this happens, isn't there a memory leak that occurs? The memory allocated to store the old value of the environment variable isn't freed, but the pointed to C-string changes. And if this occurs in the middle of the list, the list seems to be truncated (the next element in the list is set to NULL, which denotes the end of the list). Is this intentional?

For your implementation of unsetenv:

I think that the same memory leak concern applies here as well.

Also, in my copy of the book, this exercise includes the following:

Your version of unsetenv() should check to see
whether there are multiple definitions of an environment variable, and remove
them all (which is what the glibc version of unsetenv() does).

But I think the current implementation will only remove one (the first) instance of the environment variable.

The original question is wrong, cite errata, page 210

In the second sentence of exercise 1, change:

Assuming that the clock_t value returned by times() is an unsigned 32-bit integer
to:

Assuming that the clock_t value returned by times() is a signed 32-bit integer