libtrash - a shared library which implements an 'intelligent', highly
-------- configurable "recycle bin" or "trash can" under GNU/Linux.



Written by Manuel Arriaga (marriaga at stern dot nyu dot edu).

Copyright (C) 2001, 2002, 2003, 2004, 2006, 2007 Manuel Arriaga Licensed
under the GNU General Public License version 2. See the file COPYING for
details.


Version: 3.2 (2008/Jan/23)
-------

IMPORTANT NOTE on Firefox:
-------------------------

On some systems, due to some mysterious interaction, Firefox segfaults if
libtrash is enabled. I do not know how to solve this. (I guess it is a
problem in the linker rather than in libtrash or Firefox, but I haven't
looked into it.) The simple way around this problem is to disable libtrash for
Firefox. Do so by starting Firefox with the command "LD_PRELOAD= firefox".
You can bind this command (if necessary by placing it in a one-line bash
script file by itself) to whatever GUI icon or hotkey combination you use
to start Firefox.

REQUIREMENTS:
------------

- (POSSIBLY) /proc filesystem: to run libtrash in most recent systems, you
need to be running a kernel with support for the /proc file system
(CONFIG_PROC_FS). Do not worry, since compilation will fail with a warning
if this requirement applies to you and you don't have it enabled.

- To *compile* libtrash, you need both Perl as well as Python.


DESCRIPTION:
-----------

libtrash is a shared library which, when preloaded, will intercept calls to
a series of GNU libc functions and make sure that, if an attempt to destroy
certain files is made, these won't be permanently destroyed but rather moved
to a "trash can". It also allows the user to mark certain directories as
"unremovable", which means that calls to functions which would result in the
loss of files under these directories will always fail, leaving those files
untouched in their original locations.

(This last feature is meant as a higher-level substitute for ext2fs'
"immutable" flag for use by those of us who rely on other file systems. An
important difference is that libtrash allows non-privileged users to use
this with their personal files.)

The GNU libc functions which can be overriden/"wrapped" are

- unlink() / unlinkat();
- rename() / renameat();
- fopen() / fopen64();
- freopen() / freopen64();
- open() / openat() / open64() / openat64() / creat() / creat64().

You can individually enable / disable each of these "protections"; by
default, only calls to the first two functions are intercepted.

----------------------------------------------------------------------------

IMPORTANT NOTE 1: The wrappers of the "open functions" (fopen, freopen and
open) behave differently from the real functions in an important way when
they are asked to open - in either write-mode or read-plus-write-mode - a
file considered "worthy" of having a copy of itself stored in the trash can
before being truncated: while the functions in GNU libc require
write-permission to that already existing file for the call to succeed,
these wrappers require write-permission to the DIRECTORY WHICH HOLDS THAT
FILE instead. This is so because, in fact, we are renaming the existing file
before opening it, and calls to rename() require write-permission to the
directory which holds the file for them to succeed. Usually, you only have
write-permission to files in directories to which you also have
write-permission, so this shouldn't be a huge problem in most cases.

IMPORTANT NOTE 2: When a file on a partition / filesystem other than the one
in which your trash can resides is destroyed, libtrash can't just use the
GNU libc function rename() to move it into your trash can: it must copy that
file byte-after-byte into your trash can and then delete the original. To
achieve that, read-permission to the destroyed file is required. Since in
most situations you don't have write-permission to a directory which holds
files you can't read, hopefully that won't prove a big problem, either.
However, be warned that copying a file (especially a large one) will take a
lot longer than the time which would be required to simply rename it.

IMPORTANT NOTE 3: If you are running a web (or other) server as user
'nobody', then you should ensure that libtrash is not active for that
process. The issue is that by default libtrash refuses to remove files if
it will not be able to save them in that user's trash can. The 'nobody'
account typically lacks a (writable) home directory; as such, when processes
run as 'nobody' try to remove a file, libtrash will always make that
operation fail. For that reason, always start servers run through the
'noboby' account (or any other, 'low privileges' account missing a writable
home dir) with libtrash disabled (just prefix "LD_PRELOAD= " to the command
line). (My thanks to Nicola Fontana for pointing this out!)


----------------------------------------------------------------------------


libtrash works with any GNU/Linux program, both at the console and under
XFree86, and operates independently of the programming language the program
was written in. The only exception are statically linked programs, which you
probably won't find. It can be extensively configured by each user through a
personal, user-specific configuration file.

Although libtrash itself was written in C, the installation procedure
requires both Perl and Python (sorry!).


HOW libtrash WORKS / FEATURES:
-----------------------------

libtrash recreates the directory structure of your home directory under the
trash can, which means that, should you need to recover the mistakenly
deleted file /home/user/programming/test.c, it will be stored in
/home/user/Trash/programming/test.c. If you have instructed libtrash to also
store copies of files which you delete in directories outside of your home
dir (see libtrash.conf for details), they will be available under
Trash/SYSTEM_ROOT. E.g.: after deletion by the user joe, /common-dir/doc.txt
will be available at /home/joe/Trash/SYSTEM_ROOT/common-dir/doc.txt.


When you try to delete a file in a certain directory where you had
previously deleted another file with the same name, libtrash stores the new
file with a different name, in order to preserve both files. E.g.:

$ touch test
$ rm test
$ ls Trash/ test
$ touch test
$ rm test
$ ls Trash/
test test[1] <-- The file we deleted first wasn't lost.

libtrash keeps generating new names until no name collision occurs. The
deletion of a file never causes the permanent loss of a previously "deleted"
file.


Temporary files can be automatically "ignored" and really destroyed.


You can define whether you wish to allow the definitive removal of files
already in your trash can while libtrash is active. Allowing this has one
major disadvantage, which is explained in libtrash.conf. But, on the other
hand, if you don't allow the destruction of files already in your trash can,
when you need to recover HD space by permanently removing files currently
found in your trash can you will have to temporarily disable libtrash first
(instructions on how to achieve this can be found below).

To avoid the accumulation of useless files in your users' trash cans, it is
probably wise to run the script cleanTrash regularly (perhaps from a cron
job). This Perl script was kindly provided by Daniel Sadilek and works by
removing the oldest files from each trash can in your system whenever that
trash can grows beyond a certain disk size. It is meant to be run by root.
cleanTrash, together with the license according to which it can be
distributed and a short README file written by me, can be found under the
directory "cleanTrash".


You can also choose whether files outside of your home directory, hidden
files (and files under hidden directories), backup and temporary files used
by text editors and files on removable media should be handled normally or
"ignored" (i.e., you can decide if copies of such files should be created in
your trash can if the originals are about to be destroyed). It is also
possible to discriminate files based on their names' extensions: you can
instruct libtrash, e.g., to always ignore object files (files with the
extension ".o", meaning that deleting files of this type won't result in
the creation of copies of these in your trash can. By default, besides
object files, TeX log and auxiliary files (".log" and ".aux", respectively)
are also ignored.


The user may also configure libtrash to print a warning message to stderr
after each "dangerous" function call while libtrash is disabled. This
feature is meant to remind the user that libtrash is disabled and that, for
that reason, any deletions will be permanent. This feature is disabled by
default, so that libtrash remains "invisible" to the user.


Other options: name of trash can, name of TRASH_SYSTEM_ROOT under your trash
can, whether to allow the destruction of the configuration file used by
libtrash, and what to do in case of error. You can also set in your
environment a list of exceptions to the list of unremovable directories.


To configure libtrash so that it better suits your purposes you should edit
the file libtrash.conf before compiling. Even if you won't be configuring
libtrash at compile-time, it is recommended that you at least read
config.txt so that you know how libtrash handles its configuration files.



CONFIGURING, COMPILING, INSTALLING AND ACTIVATING libtrash:
----------------------------------------------------------


To configure:


1 - Edit the file libtrash.conf. All options are (verbosely) explained
there. If you want to learn about the different features libtrash offers,
that is where you want to look; otherwise just check that the default
settings look ok to you.


To compile:

2 - Run "make".



To install:

3- Edit the Makefile, possibly choosing alternative locations for the shared
library and the system-wide, uneditable configuration file (defaults:
/usr/local/lib and /etc/libtrash.conf, respectively).

4- Run, as root, "make install".

This installs libtrash in the directory specified at the top of the
Makefile, runs ldconfig and puts a system-wide configuration file in
/etc/libtrash.conf reflecting the compile-time defaults used. NEVER EDIT
THIS FILE. USE A PERSONAL CONFIGURATION FILE INSTEAD.

[Note that you can also install libtrash on your home directory: just edit the top of the file src/Makefile and run 'make install' from your account.]

5- Now go and read config.txt.



To activate libtrash:

6 - So that calls to the different GNU libc functions are intercepted, you
must "preload" this library. What I have found to be the best way to do this
is to configure your shell so that:

* the environment variable LD_PRELOAD is set to the path to
the libtrash library

* alias the "su" command to "su -l"

If you use Bash, this translates into adding the following two lines to one
of Bash's initialization files (/etc/profile or ~/.profile):

export LD_PRELOAD=/usr/local/lib/libtrash.so
alias su="su -l"

Notice that you should replace the path in the first line with the location
of libtrash on your system. (If you installed it in the default place you do
not need to edit it.)

The second line merely ensures that if you su into a different account the
LD_PRELOAD variable will also be set. (This is important to avoid nasty
surprises!) At least on my system, and unlike what some of the documentation
suggests, passing the option "-" to su is NOT enough to get LD_PRELOAD
correctly set in the new shell. The "-l" option, which some say is
equivalent to "-", does the trick for me.


TESTING libtrash:
----------------


libtrash should now be set up and ready to spare you a lot of headaches. You
can test drive it by doing the following (assuming that you didn't change
TRASH_CAN to a string other than "Trash":

1) Create a file called test_file
2) Open test_file with a text editor, type a few characters and save it.
3) Run the following commands:

$ rm test_file
$ ls Trash/

test_file should now be stored in Trash/. But don't be fooled by this
example! libtrash isn't restricted to "saving" files which you explicitly
deleted with "rm": it also works with your (graphical) file manager, mail
user agent, etc...

NOTE 1: Simply "touching" a test file -- ie, "touch test_file" -- and then
removing it will no longer put it in the trash can, because libtrash now
ignores empty files, since their removal doesn't present a risk of data
loss.

NOTE 2: To make sure that you are fully covered even when su'ing into other
accounts, you can try the following (this assumes you can su into the root
account on this machine and that you are using Bash):

$ su -c "set|grep LD_PRELOAD"

If a line like

LD_PRELOAD=/usr/local/lib/libtrash.so

is shown that means you are all set! (If not, see the previous section on
how to make sure that su sets the LD_PRELOAD environment variable.)


SUSPENDING/RESUMING/CIRCUMVENTING libtrash:
------------------------------------------


Should you need to temporarily disable libtrash, you can do so by running
the command

$ export TRASH_OFF=YES

When you are done, libtrash can be reactivated by typing:

$ export TRASH_OFF=NO

You might make these operations simpler by appending the following two lines
to the init file you used in step 5) above (if you are using Bash as your
shell):

alias trash_on="export TRASH_OFF=NO"
alias trash_off="export TRASH_OFF=YES"

After doing so, you can enable/disable libtrash by typing

$ trash_on

or

$ trash_off

at the prompt.

If you often need to remove one or more files in a definitive way using
'rm', you might wish to define

alias hardrm="TRASH_OFF=YES rm"

After having done so,

hardrm file.txt

will achieve the same effect as

TRASH_OFF=YES rm file.txt

NOTE: I strongly advise AGAINST defining such an alias, because you will
probably get into the habit of always using it: at the time you delete a
file, you are always sure that you won't need it again... :-) The habit of
using that alias effectively makes installing libtrash useless. Unless you
wish to effectively do away with the file due to privacy/confidentiality
concerns, think instead of how cheap a gigabyte of HD space is! :-)

If you have set the option SHOULD_WARN (see libtrash.conf), running a
command while TRASH_OFF is set to "YES" will result in libtrash printing to
stderr (at least) one reminder that it is currently disabled.



LIMITATIONS:
-----------

1- As mentioned in the second note near the top of this document, destroying
documents in a partition different from the one on which your home directory
resides will result in a byte-after-byte copy of those files into your trash
can. If I could think of a faster, more efficient way of doing that I would
have already implemented it. Unfortunately, things like quota-support and
access permissions make this problem hard to solve. Unless someone suggests
a good way to overcome this, this isn't going to change any time soon...
Sorry!

2- As mentioned in the section on how to activate libtrash, the LD_PRELOAD
method doesn't protect you from mistakes while using an account in which
(for any reason) LD_PRELOAD isn't set and pointing to libtrash. If you 'su'
into other accounts, you should (i) make sure that, by default, they have
LD_PRELOAD pointing to libtrash and (ii) always use "su - [user name]",
instead of "su [user name]". The only alternative is to activate libtrash
from /etc/ld.so.preload.