Learning the MaterialIndex
I was watching a student on the #95 bus running through her hand-made flashcards to help memorize anatomy. Every card had a photocopied and pasted picture of some muscle groups on the front with identifying letters, and on the back-side were long, hand-written notes about what each lettered group was. Those cards must have taken her hours to make, and rather than play video games on her phone she was reviewing them on the ride home. Some students are truly determined to succeed. Have you made Linux flash cards to memorize Linux commands and options?
Do you want to know Linux? Are you in the right field?
Some CommandsIndex
Keep a notebook with a List of Commands in it.
Why doesn’t this work? (See Worksheet #05 section 5.3.)
$ touch lab5.3b
$ rm lab5.[3b]
Changes by Ubuntu to the basic Unix security model for symlinks and hard links:
- Overview: http://utcc.utoronto.ca/~cks/space/blog/linux/Ubuntu1204Symlinks
- “In the standard kernel, this […] blocks hardlinks to devices, setuid files, executable setgid files, and files that the UID making the link cannot read or write to (except that the owner of a file is always allowed to make hardlinks to it). Note that this blocks hardlinks to other people’s world-readable files if you can’t write to them.”
- http://lwn.net/Articles/390323/
- “But some kernel hackers are not convinced that the core kernel should be fixing badly written applications.”
- http://utcc.utoronto.ca/~cks/space/blog/linux/Ubuntu1204Symlinks
- “Both the Ubuntu Yama LSM and the new standard kernel code for this stuff include a second restriction, this time on what can be hardlinked.”
- Code patch and descriptions: http://lwn.net/Articles/393012/
- “Normally, hardlinks can be created to files that a given user does not have access to. This can create security problems where privileged processes act on files that only they have access to, but have been put places unexpectedly by an attacker. This option limits the creation of hardlinks to files that a given user would be unable to read and write originally, or are not otherwise sensitive.”
- Change behaviour:
sysctl -w kernel.yama.protected_sticky_symlinks=0
- Change behaviour:
sysctl -w kernel.yama.protected_nonaccess_hardlinks=0
A useful option to ls -l is -L - dereference (follow, expand) symlinks and show the real thing:
$ ls -dils /bin/*sh
524294 936 -rwxr-xr-x 1 root root 955024 Apr 3 2012 /bin/bash
524318 108 -rwxr-xr-x 1 root root 109768 Mar 29 2012 /bin/dash
524419 0 lrwxrwxrwx 1 root root 4 Sep 7 00:22 /bin/rbash -> bash
524434 0 lrwxrwxrwx 1 root root 4 Sep 7 00:22 /bin/sh -> dash
524438 0 lrwxrwxrwx 1 root root 7 Sep 7 00:22 /bin/static-sh -> busybox
$ ls -dilsL /bin/*sh
524294 936 -rwxr-xr-x 1 root root 955024 Apr 3 2012 /bin/bash
524318 108 -rwxr-xr-x 1 root root 109768 Mar 29 2012 /bin/dash
524294 936 -rwxr-xr-x 1 root root 955024 Apr 3 2012 /bin/rbash
524318 108 -rwxr-xr-x 1 root root 109768 Mar 29 2012 /bin/sh
524297 1788 -rwxr-xr-x 1 root root 1827920 Apr 13 2012 /bin/static-sh
$ ls -dilsL /bin/*sh | sort
524294 936 -rwxr-xr-x 1 root root 955024 Apr 3 2012 /bin/bash
524294 936 -rwxr-xr-x 1 root root 955024 Apr 3 2012 /bin/rbash
524297 1788 -rwxr-xr-x 1 root root 1827920 Apr 13 2012 /bin/static-sh
524318 108 -rwxr-xr-x 1 root root 109768 Mar 29 2012 /bin/dash
524318 108 -rwxr-xr-x 1 root root 109768 Mar 29 2012 /bin/sh
- A useful option to
find is -ls – display full pathname information similar to ls -lids:
- A useful option to
find is -links – find by number of links:
$ find /lib -type f -links +1 -ls
- A useful option to
find is -inum – find by inode number:
$ find /lib -inum 171600 -ls
Author:
| Ian! D. Allen - idallen@idallen.ca - Ottawa, Ontario, Canada
| Home Page: http://idallen.com/ Contact Improv: http://contactimprov.ca/
| College professor (Free/Libre GNU+Linux) at: http://teaching.idallen.com/
| Defend digital freedom: http://eff.org/ and have fun: http://fools.ca/
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