ulimit

UNIX for Advanced & Expert Users
1

hi

what is the difference between file and data? if file is unlimited, does that mean we can have a file as big as we like?

thanks.

file(blocks) unlimited
data(kbytes) 1048576

2

data is the size of the data segment of a process. This is similiar to stack which is a limit on the stack segment of a process. file is the limit of a data file on disk (or more generally, a file in a filesystem).

unlimited means that the ulimit facility imposes no artificial limit of its own. But everything in a computer is finite. Eventually you will bump into some other limit.

3

thanks a lot

4

There are two limits on files - the total number of files you can have open at one time, and the max size of a file. The number of open files depends on things like kernel settings and your OS. The max size of a file usually depends on whether your system can support files larger than 2GB. Of course you have to have free disk space.....

5

thanks jim,

i jabe heard this before, of a file not being able to be bigger than 2G. Is this because this is the default? If my ulimit for file is set to say 10G, then can I create a file bigger than 2G? Or are there some other programs that also have limits set to 2G, so even if I created it for 5G on my unix box, it might still give me some problems?

thanks

6

There are various file system types that have inherent limits. cdrfs jfs jfs2 etc. So as you build a unix system you need to be aware of the limitations of the various filesystem types. Each of them will have upper limits on inode numbers file sizes etc.

7

Files bigger than the number of bytes that a 32 bit integer can reference are usually called largefiles. Most modern UNIX-es have support for it with either oddly-named non-standard calls like fopen64() or some kind of more modern filesystem.

If you have LARGEFILE support and no disk quota enabled, you can essentially create a file that has size equal to the free space available on the disk. This is a BAD idea in general. sysadmins love to hate giant files, especially small files with giant holes in them....