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File System, Part 3: Permissions

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angrave edited this page Nov 7, 2014 · 20 revisions

Under construction

How can I have the same file appear in two different places in my file system?

(From code? Command?) Reference counting?

What happens when I rm (remove) a file?

rm = unlinking?

How do I change the permissions on a file?

chmod 644 /bin/sandwhich
chmod 755 /bin/sandwhich
chmod ugo-w /bin/sandwhich
chmod o-rx /bin/sandwhich

How do I read the permission string from ls?

What is sudo?

How do I change ownership of a file?

How do I set permissions from code?

chmod(const char *path, mode_t mode);

Why are some files 'setuid' what does this mean? ?

set-user-ID-on-execution/set-group-ID-on-execution Why are they useful?

What permissions does sudo run as ?

ls -l /usr/bin/sudo
-r-s--x--x  1 root  wheel  327920 Oct 24 09:04 /usr/bin/sudo

What's the difference betweeen getuid() and geteuid()?

How do I ensure only privileged users can run my code?

Use geteuid() == 0

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