Для чего существует директория /var/log в Линукс,и почему она столько места жрет?

ничего, что на английском страяпал да?)) )

FOLDER USE

-OS-space -- only cruical os components are stored in this folders.
/boot Contains important files to boot the computer including the bootloader configuration and the kernel.
/binGlobal software, necessary for OS function is stored here.
/sbin Global software, necessary for OS function, and can cause damage (only be run by the superuser) is stored here.
/dev Each device on your system (such as sound cards, Webcams etc) has an entry in this folder. Each application accesses the device by using the relevant items inside /dev.
/lib Important system software libraries are stored here. Hardware and high importance systemwide libraries.
/media Media devices such as CD drives and USB sticks are referenced here when they are plugged in. More on this later.
/mnt Other devices can be mounted later.
/opt Optional software can be installed here. This folder is usually used when you want to build you own software. If you don't build your own software, you ignore this folder.
/procprocesses.
/sys Information about current running status of the system is stored here.
/root This is the home directory for the main superuser.
/tmpTemporary files location. Contents are auto-deleted on system poweron.

/etc Systemwide configuration files,default and global settings for the software installed on your system are stored here.
/var This folder contains log files about the software on your computer.

-Global User-space -- user software is stored here
/usr/bincontains binaries or links for globally accessible user software.
/usr/sbincontains binaries or links for globally accessible superuser-only software.
/usr/gamesseems everyone wishes to separate game binaries from others...
/usr/libglobal,nonsystem software (shared) libraries.
/usr/shareglobal,nonsystem software data is installed here, contains a lot of systemshared resources. icons,sounds etc.
/usr/local/contains a special copy of /usr. software/things that are temporary or alternative or wished to be separated, goes here. Not to mess the system.

-Local User-space -- per-account personal software/settings/things are stored here
/home Each user account on the system has a home directory, and they are stored here.
/home/<account>local configurations are stored here. They normaly override those global in /etc/*
/home/<account>/.locallocal software installations is stored here. This software is ONLY accessible from specific account.

логи тама :)))

Сделай ls -alh /var/log, не должна много жрать вообщето. Ровным счетом насколько мегабайт и все.
logrotate стоит? Настроен?

логи ...отслеживание происходящего в системе
чисть времея от времени ...либо ваще отруби службы типо syslog-ng еслиф не увлекаешся чтением))

>>логи ...отслеживание происходящего в системе
А жрет много, потому, что куча лишней инфы сохраняется. например: инфо о каждом обращении к веб серверу, при хорошей посещалке сайта, бешенные цыфры получаются.
Настраивать надо