chmod -x chmod
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Video at http://www.youtube.com/watch?v=DTWZqh64RcQ. You're in a Data Center, with absolutely no contact with the outside world, with a machine that you must not restart, and someone performed a `chmod -x chmod`. This is a problem we used in interviews during 2009, and this presentation is a list of some of the possible solutions that my co-workers at SAPO have suggested.
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chmod -x chmod
- 1. chmod -x chmod José Castro <cog@cpan.org> August 2010
- 2. During 2009 we posed this problem to several of our candidates
- 3. You’re in a Data Center
- 4. With absolutely no contact with the outside world
- 5. There’s a machine you must not reboot
- 6. And someone had the brilliant idea of performing a `chmod -x chmod`
- 8. The following is a list of possible solutions proposed by my co-workers
- 9. If the package is in cache, reinstall it
- 10. On Debian: sudo apt-get install --reinstall coreutils
- 11. Use a language that implements chmod
- 12. Perl perl -e ‘chmod 0755, “chmod”’
- 13. Python python -c "import os;os.chmod('/bin/chmod', 0777)"
- 14. d un teste Node.js require("fs").chmodSync("/bin/chmod", 0755);
- 15. Use existing executables or create your own
- 16. $ cat - > chmod.c
- 17. $ cat - > chmod.c int main () { } ^D
- 18. $ cat - > chmod.c int main () { } ^D $ cc chmod.c
- 19. $ cat - > chmod.c int main () { } ^D $ cc chmod.c $ cat /bin/chmod > a.out
- 20. $ cp cat new_chmod $ cat chmod > new_chmod
- 21. $ cat - > restore_chmod.c
- 22. $ cat - > restore_chmod.c #include <sys/types.h> #include <sys/stat.h> int main () { chmod( "/bin/chmod", 0000777 ); } ^D
- 23. $ cat - > restore_chmod.c #include <sys/types.h> #include <sys/stat.h> int main () { chmod( "/bin/chmod", 0000777 ); } ^D $ cc restore_chmod.c
- 24. $ cat - > restore_chmod.c #include <sys/types.h> #include <sys/stat.h> int main () { chmod( "/bin/chmod", 0000777 ); } ^D $ cc restore_chmod.c $ ./a.out
- 25. launch BusyBox (it has a chmod inside)
- 26. GNU tar
- 27. $ tar --mode 0777 -cf chmod.tar /bin/chmod $ tar xvf chmod.tar
- 28. tar --mode 555 -cvf - chmod | tar xvf -
- 29. d un teste $ tar -cvf chmod.tar chmod edit the archive and alter the permissions
- 30. “You said I couldn’t go to the internet...
- 31. “You said I couldn’t go to the internet... but you said nothing about the other machines on the data center...”
- 32. Open a socket to another machine and do a: $ tar --preserve-permissions -cf chmod.tar chmod
- 33. Open a socket to another machine and do a: $ tar --preserve-permissions -cf chmod.tar chmod Get this tar to your machine and: $ tar xvf chmod.tar
- 34. cpio
- 35. cpio lets you copy files to and from archives
- 36. bytes 19 to 24 are the file mode (http://4bxf.sl.pt)
- 37. echo chmod | cpio -o | perl -pe 's/^(.{21}).../${1}755/' | cpio -i -u
- 38. Hardcore
- 40. d un teste • attrib or ls -@ • force the inode into cache • check kcore for the VFS structures • use sed to alter the execution bit without the kernel realizing it • run chmod +x chmod
- 41. Text editors sometimes need to overwrite a file
- 42. Thus, some of them have something resembling chmod
- 43. Emacs
- 44. Ctrl+x b > *scratch* (set-file-modes "/bin/chmod" (string-to-number "0755" 8)) Ctrl+j
- 45. There seem to be countless solutions
- 46. But one of the best answers I’ve seen...
- 47. Was from a guy who replied to my “Solve the problem” with...
- 48. “What problem? Isn’t the machine still running?”
- 49. The End (for now)