unix

VNC

vncserver –geometry 1200x1000 :8

You will require a password to access your desktops.

Would you like to enter a view-only password (y/n)? n

xauth: creating new authority file /root/.Xauthority

New 'X' desktop is coe-he-81:1

Creating default startup script /root/.vnc/xstartup

Starting applications specified in /root/.vnc/xstartup

Log file is /root/.vnc/coe-he-81:1.log

On Windows there is RealVNC, TightVNC

http://shebang.brandonmintern.com/tips-for-remote-unix-work-ssh-screen-and-vnc

http://www.nomachine.com/ Client and Server

http://computingplugs.com/index.php/Installing_FreeNX_server_and_NX_Open_Source_Components

http://www.xrdp.org/

X stack explained

http://blog.mecheye.net/2012/06/the-linux-graphics-stack/

http://habrahabr.ru/post/148954/

Belkin KVM switch

http://synergy2.sourceforge.net/

SCP

scp [options] [[user@]host1:]filename1 ... [[user@]host2:]filename2

scp -r dvader@deathstar.com:somedir somedir

When using wildcards (e.g., * and ? ) to copy multiple files from a remote system, be sure to enclose the filenames in quotes. This is because the Unix shell, not the scp command, expands unquoted wildcards.

File descriptors: 1 for stdout, 2 for stderr, 0 for stdin

ls -al 1>file1.txt 2>file2.txt

Save the output to a file and at the same time echo everything to the screen:

ls -al | tee blah.txt

Redirect standard error to point to the same place as stdout and then we pipe the whole mess to tee in order to both save and echo at the same time:

ls -al 2>&1 | tee blah.txt

command 2>&1 > file # <---- do not use this http://en.wikipedia.org/wiki/Redirection_%28computing%29

command > file 2>&1 # use this

Soft and hard links

Hard links may not normally point to directories and they cannot link paths on different volumes. This has the effect of creating multiple names for the same file, causing an aliasing effect: if the file is opened by one of its names, and changes are made to its content, then these changes will also be visible when the file is opened by an alternative name.

By contrast, a soft link on such file systems is not a link to a file itself, but to a file name; this also creates aliasing, but in a different way.

Hard Link

An hard link refers directly to the physical location of another file (an inode to be precise).

A hard link has some limitations: it cannot refer to a directory and cannot cross file system boundaries. It means that you can only create hard links to the same file system where the hard link is located.

When the source of the link is moved or removed, the hard link still refer to the source.

Symbolic link are created with the ln command. For instance, to create a link to source_file:

Symbolic Link

A symbolic link refers to a symbolic path indicating the location of the source file. You can see it as a link to a path (itself refering to an inode).

A symbolic link is less limited. It can refer to a directory and can cross file system boundaries.

However, when the source of the link is moved or removed, the symbolic link is not updated.

Symbolic link are created with the ln command. For instance, to create a symbolic link to source_file:

Deletion

The deletion of a link (hard or symbolic) can be achieved with the rm or unlink commands:

Hard Links : 1. All Links have same inode number. 2. ls -l command shows all the links with the link column (Second) shows No. of links. 3. Links have actual file contents 4.Removing any link just reduces the link count but doesn't affect other links.

http://ru-linux.livejournal.com/2878030.html#commentsSoft Links(Symbolic Links) : 1.Links have different inode numbers. 2. ls -l command shows all links with second column value 1 and the link points to original file. 3. Link has the path for original file and not the contents. 4.Removing soft link doesn't affect anything but removing original file the link becomes dangling link which points to non-existant file.

You can create hard links only for files and not for directories. A symbolic link merely contains a text string that is interpreted and followed by the operating system as a path to another file or directory.

It is a file on its own and can exist independently of its target. If a symbolic link is deleted, its target remains unaffected. If the target is moved, renamed or deleted, any symbolic link that used to point to it continues to exist but now points to a non-existing file.

Symbolic links pointing to non-existing files are sometimes called broken, orphaned, dead or dangling.

On many systems today, the ls command is aliased to ls --color=auto

Without color, you need more information, such as that provided by a long listing using ls -l

In the first column of output, you see the first character is an 'l' (lower-case L) for symbolic links

Using find to locate symlinks:

$ find foo -type l

Symlinks do not prevent a file from being deleted; if the target file is moved or deleted, then the symlink will be broken. For this reason, many systems use colors in directory listings, often pale blue for a good link and red for a broken one.

Soft links, or symlinks, merely point to another file or directory by name rather than by inode. Soft links can cross file system boundaries.

Deleting a soft link does not delete the target file or directory, and deleting the target file or directory does not automatically remove any soft links.

You will get an error if you attempt to create hard links that cross file systems or that are for directories.

You use the ln command with the -s option to create soft links. Soft links use file or directory names, which may be relative or absolute.

http://www.ibm.com/developerworks/linux/library/l-lpic1-v3-104-6/index.html

Linking

http://eli.thegreenplace.net/2013/07/09/library-order-in-static-linking/

http://lwn.net/Articles/276782/

http://habrahabr.ru/post/192264/

Дальше подключаются функции из libdl.so и поиск нужно библиотеки идет с учетом

строк в файле /etc/ld.so.conf, /etc/ld.so.preload, переменных LD_LIBRARY_PATH и

LD_PRELOAD и в кэше /etc/ld.so.cache, и некоторых других, зависящих от системы и glibc, условий.

Напомню, ld.so.cache формируется утилитой ldconfig, с учетом путей указанных в

/etc/ld.so.conf. Порядок обхода путей поиска совпадает с последовательностью,

указанной в этом файле.

LD_PRELOAD

http://jvns.ca/blog/2014/11/27/ld-preload-is-super-fun-and-easy/

http://www.catonmat.net/blog/simple-ld-preload-tutorial-part-2/

http://adamjsho.blogspot.co.uk/2013/11/subverting-library-calls-with-ldpreload.html

http://blog.mmalecki.com/2013/07/17/using-ld-preload.html

http://habrahabr.ru/post/199090/ LD_PRELOAD

http://news.ycombinator.com/item?id=4375493

http://www.linuxforu.com/2011/10/gnu-binutils-collection-of-binary-tools/http://zachsaw.blogspot.com/2012/10/gcc-linker-library-flag-order.html

http://shmat-razum.blogspot.com/2010/12/blog-post.html

http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html

http://www.macieira.org/blog/2012/01/sorry-state-of-dynamic-libraries-on-linux/http://cseweb.ucsd.edu/~gbournou/CSE131/the_inside_story_on_shared_libraries_and_dynamic_loading.pdf

http://www.linuxforu.com/2011/12/loading-library-files-in-cpp/http://techblog.rosedu.org/library-management.html

http://www.lurklurk.org/linkers/linkers.html

http://habrahabr.ru/post/150327/

http://www.geeksforgeeks.org/working-with-shared-libraries-set-2/

http://www.ibm.com/developerworks/linux/library/l-lpic1-v3-102-3/index.html

http://www.iecc.com/linker/

http://www.reddit.com/r/programming/comments/9367k/in_linux_whats_the_difference_between_an_object/

SHARED LIBRARIES:

http://blog.markloiseau.com/2013/01/linux-shared-object-tutorial/#more-1855

http://www.ibm.com/developerworks/linux/library/l-setup-sharedlibs-pr/index.html

http://amir.rachum.com/blog/2016/09/17/shared-libraries/

https://lwn.net/Articles/631631/

http://www.cyberciti.biz/tips/linux-shared-library-management.htmlhttp://www.cprogramming.com/tutorial/shared-libraries-linux-gcc.html

http://www.akkadia.org/drepper/dsohowto.pdf

Applications in Linux are linked to an external function in one of two ways: either statically linked at build time, with static libraries (lib*.a) and having the library code include in the application's executable file, or dynamically linked at runtime with shared libraries (lib*.so)

http://habrahabr.ru/blogs/cpp/132300/

Two types of executable programs:

- Statically linked executables contain all the library functions that they need to execute; all library functions are linked into the executable.

- Dynamically linked executables; ldd command shows the shared library dependencies

How does the dynamic loader know where to look for executables?

There is a configuration file in /etc. In fact, there are two configuration files, /etc/ld/so/conf and /etc/ld.so.cache. Older systems may have all entries in /etc/ld/so/conf and not include entries from the /etc/ld.so.conf.d directory.

The ldconfig command creates the necessary links and cache to recently used shared libraries in /etc/ld.so.cache.

The dynamic loader uses the cached information from ld.so.cache to locate files that are to be dynamically loaded and linked.

If you change ld.so.conf (or add new included files to ld.so.conf.d), you must run the ldconfig command (as root) to rebuild your ld.so.cache file.

If you're running an older application that needs a specific older version of a shared library, you might want to override the default search paths used by the loader.

Just as you can set the PATH variable to specify a search path for executables,

You can set the LD_LIBRARY_PATH variable to a colon-separated list of directories that should be searched for shared libraries before the system ones specified in ld.so.cache.

For example:

export LD_LIBRARY_PATH=/usr/lib/oldstuff:/opt/IBM/AgentController/lib

If you have a compelling reason to add a path to many programs, you can also change the system's default search path.

The dynamic linker is controlled through /etc/ld.so.conf, which contains a list of directories to search by default.

Any paths specified in LD_LIBRARY_PATH will be searched before the paths listed in ld.so.conf, so users can override these settings.

To prevent users (and programmers) from needing to track library numbers and updates, the system comes with a large number of symbolic links.

In general, the pattern is that libexample.so will be a link to libexample.so.N

For every major version number supported, libexample.so.N will be a link in turn to libexample.so.N.M

If you specify -lexample to the linker, it looks for libexample.so which is a symbolic link to a symbolic link to the most recent version.

In a traditional static library, the code generated is usually bound together into a library file with a name ending in .a and then it's passed to the linker.

In a dynamic library, the library file's name generally ends in .so.

A normal static library is in a format created by the ar utility, which is basically a very simple-minded archive program, similar to tar but simpler.

In contrast, shared libraries are generally stored in more complicated file formats.

When linking a program, you can specify additional paths to search at runtime. In gcc the syntax is -Wl,-R/path

You can use ldd to list all the dynamic link lib dependencies: ldd /path/to/your/app However this shows direct and indirect (i.e. those needed by other libraries) dependencies, so you can tell what are just the direct dependencies by using readelf: readelf -d /path/to/your/app The direct dependencies are the libraries listed as NEEDED. Linking to different versions of a dynamic library On Linux there's loads of [dynamic ".so"] libraries in places like /usr/lib. The libraries have version numbers; Major version indicates major (API) changes, whilst the minor version typically relates to bug fixes. These version numbers are firstly enshrined with the library using a special symbol (SONAME) - which is assigned on library creation (using the -soname arg to ld). Also libraries are named with their version numbers libsomething.so.2.3. You can verify this using: objdump -p libsomething.so.2.3* | grep SONAME So if you're developing and you want to link to specific version what do you do? Well basically there's no neat trick to get the linker (ld) to link a specific version at compile time :( so you can either: Link using the full path to the specific library version Create a softlink/symlink (ending in ".so" - with NO version) to the specific library version ldconfig does do some stuff related creating links for libraries but as explained here it won't create the plain ".so" necessary for development - these are usually included as part of a "dev" (usually suffixed by "-dev") package on your system (be it Debian or Red Hat or whatever).

http://www.openlogic.com/wazi/bid/332308/Become-a-GCC-expert-with-these-little-known-command-line-options

Compiling 32-bit apps on 64-bit Linux

$ gcc -m32 hello.c -o hello

$ file hello

hello: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.8, not stripped

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