You may either call the mount command and parse its output to find the longest common prefix with your path, or use the stat system call to get the device a file resides on and go up the tree until you get to a different device. In Python, stat may be used as follows (untested … Read more
Your code is ignoring SIGSEGV instead of catching it. Recall that the instruction that triggered the signal is restarted after handling the signal. In your case, handling the signal didn’t change anything so the next time round the offending instruction is tried, it fails the same way. If you intend to catch the signal change … Read more
System calls are operating system functions, like on UNIX, the malloc() function is built on top of the sbrk() system call (for resizing process memory space). Libraries are just application code that’s not part of the operating system and will often be available on more than one OS. They’re basically the same as function calls … Read more
There’s an xterm control sequence for this: \e]11;?\a (\e and \a are the ESC and BEL characters, respectively.) Xterm-compatible terminals should reply with the same sequence, with the question mark replaced by an X11 color name, e.g. rgb:0000/0000/0000 for black.
When you source the file, the assignments will be set but the variables are not exported unless the allexport option has been set. If you want all the variables to be exported, it is much simpler to use allexport and source the file than it is to read the file and use export explicitly. In … Read more
You won’t be able to open a server on port 80 without root privileges, this is a restriction on the OS level. So the only solution is to drop root privileges after you have opened the port. Here is a possible solution to drop root privileges in Python: Dropping privileges in Python. This is a … Read more
It is both complicated and differs from Unix to Unix variant. In Linux, for example, a system called Futex (Short for Fast Userspace Mutex) is used. In this system an atomic increment and test operation is performed on the mutex variable in user space. If the result of the operation indicates that there was no … Read more
sed -i ‘/^$/d’ foo This tells sed to delete every line matching the regex ^$ i.e. every empty line. The -i flag edits the file in-place, if your sed doesn’t support that you can write the output to a temporary file and replace the original: sed ‘/^$/d’ foo > foo.tmp mv foo.tmp foo If you … Read more
A secure RSA encryption is implemented with an appropriate padding scheme, which includes some randomness. See PKCS#1 or OAEP for more details. The RSA encryption encrypts message padded with ‘0’s and a string of random bit. In the process, the random string is “hidden” in the ciphertext by cryptographic hashing and XORing. On decryption, the … Read more
The most reliable method I’ve come across in unix is readlink -f: $ readlink -f /x/y/../../a/b/z/../c/d /a/b/c/d A couple caveats: This also has the side-effect of resolving all symlinks. This may or may not be desirable, but usually is. readlink will give a blank result if you reference a non-existant directory. If you want to … Read more