Merge pull request #375 from Lakshmipathi/master

128K limit, chattr, rsync, other additions

README.md

@@ -184,6 +184,20 @@ Notes:
 
 - For running a command with privileges, use `sudo` (for root) or `sudo -u` (for another user). Use `su` or `sudo bash` to actually run a shell as that user. Use `su -` to simulate a fresh login as root or another user.
 
+- For a basic calculator (and of course access to Python in general), use `python` interpreter. For example,
+```
+>>> 2+3
+5
+```
+
+- File attributes are settable via `chattr` and offer a lower-level alternative to file permissions. For example, to protect against accidental file deletion the immutable flag:  `sudo chattr +i /critical/directory/or/file`
+
+- Use `getfacl` and `setfacl` to save and restore file permissions. For example: 
+```sh
+   getfacl -R /some/path > permissions.txt
+   setfacl --restore=permissions.txt
+```
+
 
 ## Processing files and data
 
@@ -238,6 +252,7 @@ Notes:
 ```sh
 mkdir empty && rsync -r --delete empty/ some-dir && rmdir some-dir
 ```
+Also use `rsync` instead of `scp`, so that after network interruption you resume the file transfer rather than restarting from scratch.
 
 - Use `shuf` to shuffle or select random lines from a file.
 
@@ -305,6 +320,10 @@ mkdir empty && rsync -r --delete empty/ some-dir && rmdir some-dir
 
 - Use `dmesg` whenever something's acting really funny (it could be hardware or driver issues).
 
+- If you delete a file and it doesn't free up expected disk space as reported by `du`, check whether the file is in use by a process: 
+`lsof | grep deleted | grep "filename-of-my-big-file"`
+
+- Know about the [128K limit](https://wiki.debian.org/CommonErrorMessages/ArgumentListTooLong) on command lines. This "Argument list too long" error is common when wildcard matching large numbers of files. (When this happens alternatives like `find` and `xargs` may help.)
 
 ## One-liners