10 ms·

Genuine question: how do you know such things? I'd love to learn them, so I'm wondering how others learn them (other than remembering random comments from here)

by AlexSW 4y ago

Genuine question: how do you know such things? I'd love to learn them, so I'm wondering how others learn them (other than remembering random comments from here).

woodruffw 4y ago
`ptrace(2)` and `userfaultfd(2)` show up when doing program tracing/analysis, among other places. I don't know of a great resource for the latter, but Eli Bendersky has a terrific series on debuggers that covers `ptrace(2)`[1]. [1]: https://eli.thegreenplace.net/2011/01/23/how-debuggers-work-part-1 https://eli.thegreenplace.net/2011/01/23/how-debuggers-work-...
- l33t2328 4y ago
  This is getting off topic but what the heck does the number in parenthesis mean on man pages?
  - 5e92cb50239222b 4y ago
    Man sections, a legacy from ye olden days when man pages were printed on paper and you'd use numbered sections for faster navigation (or splitting them into separate books if there are too many pages). For example, `man 2 select` (or `man select.2`) gives you information about the `select` syscall, and `man 3 select` has information on the libc wrapper around that syscall. A somewhat better example might be time: `time.1` has info on the command use to calculate running time of another command (in statements like `time make -j`, and `time.7` — low-level information on how to interact with kernel's time-related functionality. Since both are named `time`, if you just use `man time` without the number, you get the first one (and no way to get to the second). Read `man man`, it has a lot more on this stuff. The table below shows the section numbers of the manual followed by the types of pages they contain. 1 Executable programs or shell commands 2 System calls (functions provided by the kernel) 3 Library calls (functions within program libraries) 4 Special files (usually found in /dev) 5 File formats and conventions, e.g. /etc/passwd 6 Games 7 Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7), man-pages(7) 8 System administration commands (usually only for root) 9 Kernel routines [Non standard]
    - woodruffw 4y ago
      TIL about the `.N` suffix. I've always done `man N page`!
      - 5e92cb50239222b 4y ago
        I don't think it's very portable, actually. It doesn't work on any of the BSDs or OpenSolaris forks IIRC. A yet another alternative spelling `man 'select(2)'` should work everywhere, but many shells require you to escape parentheses (or put them in quotes as above), so I don't find it very useful.

by AlexSW 4y ago

Genuine question: how do you know such things? I'd love to learn them, so I'm wondering how others learn them (other than remembering random comments from here).

woodruffw 4y ago

`ptrace(2)` and `userfaultfd(2)` show up when doing program tracing/analysis, among other places. I don't know of a great resource for the latter, but Eli Bendersky has a terrific series on debuggers that covers `ptrace(2)`[1]. [1]: https://eli.thegreenplace.net/2011/01/23/how-debuggers-work-part-1 https://eli.thegreenplace.net/2011/01/23/how-debuggers-work-...

l33t2328 4y ago
This is getting off topic but what the heck does the number in parenthesis mean on man pages?
- 5e92cb50239222b 4y ago
  Man sections, a legacy from ye olden days when man pages were printed on paper and you'd use numbered sections for faster navigation (or splitting them into separate books if there are too many pages). For example, `man 2 select` (or `man select.2`) gives you information about the `select` syscall, and `man 3 select` has information on the libc wrapper around that syscall. A somewhat better example might be time: `time.1` has info on the command use to calculate running time of another command (in statements like `time make -j`, and `time.7` — low-level information on how to interact with kernel's time-related functionality. Since both are named `time`, if you just use `man time` without the number, you get the first one (and no way to get to the second). Read `man man`, it has a lot more on this stuff. The table below shows the section numbers of the manual followed by the types of pages they contain. 1 Executable programs or shell commands 2 System calls (functions provided by the kernel) 3 Library calls (functions within program libraries) 4 Special files (usually found in /dev) 5 File formats and conventions, e.g. /etc/passwd 6 Games 7 Miscellaneous (including macro packages and conventions), e.g. man(7), groff(7), man-pages(7) 8 System administration commands (usually only for root) 9 Kernel routines [Non standard]
  - woodruffw 4y ago
    TIL about the `.N` suffix. I've always done `man N page`!
    - 5e92cb50239222b 4y ago
      I don't think it's very portable, actually. It doesn't work on any of the BSDs or OpenSolaris forks IIRC. A yet another alternative spelling `man 'select(2)'` should work everywhere, but many shells require you to escape parentheses (or put them in quotes as above), so I don't find it very useful.