Run 'ls -l' in a directory you have problems with files. It'll show you something like
-rwxr-xr-x 1 root root 2868 sty 28 2003 arch*
lrwxrwxrwx 1 root root 4 cze 22 16:14 awk -> gawk*
-rwxr-xr-x 1 root root 11416 lis 10 22:42 basename*
-rwxr-xr-x 1 root root 625516 sty 14 2003 bash*
lrwxrwxrwx 1 root root 4 cze 22 16:14 bash2 -> bash*
-rwxr-xr-x 1 root root 15288 lis 10 22:42 cat*
It's partial output from my /bin. What's interesting? First, third and fourth column. First is for permission, third for owner and fourth for group. Permision filed canbe divided in four parts (example from the line with 'cat'):
- - special meaning. 'l' in the lines above mea they're links.
rwx - owner permissions. In this case: read(r), write(w) and execute(x)
r-x - group permissions: read(r) and execute(x)
r-x - permission for other users: read(r) and execute(x)
So if you're not owner of this file (root), you can't write it.
See how it looks like with your files.