Login or Register to Ask a Question and Join Our Community


Red Hat

Shared memory in linux

Login to Discuss or Reply to this Discussion in Our Community

 
Thread Tools Search this Thread
Operating Systems Linux Red Hat Shared memory in linux
# 1  
Old 03-16-2010
Shared memory in linux
Hello, I am using Linux os.

Code:
[tom@tattu ~]$ df -k /dev/shm
Filesystem           1K-blocks      Used Available Use% Mounted on
tmpfs                  2023256   1065000    958256  53% /dev/shm
[tom@tattu ~]$

Based on my google this, it is shared memory. What is this shared memory and where exactly it is used? Can you please help me to understand more about this?
Last edited by pludi; 03-17-2010 at 03:04 AM.. Reason: code tags, please...
# 2  
Old 03-16-2010
Shared memory is physical memory that is used by two or more different processes at the same time.

Ex: shared libraries. This is code that gets loaded into memory, and all processes running on the system see it an use it at the same time.
# 3  
Old 03-16-2010
Thanks....
# 4  
Old 03-16-2010
shared memory isn't quite the same thing as /dev/shm. shared mem can be done many ways actually. /dev/shm is essentially a RAM disk.
# 5  
Old 03-18-2010
shm/shmfs is the filesystem used by used for temporary storage as tmpfs .
/dev/shm is the physicaly shared memory from RAM which is used to speed up execution in Linux/unix . i.e. if a programme is having a portion of memory that can be shared to another programme if permitted .

We can increase our /dev/shm if we have enough RAM , for better performance .
# 6  
Old 03-20-2010
Quote:
Originally Posted by divyaimca
/dev/shm is the physicaly shared memory from RAM which is used to speed up execution in Linux/unix .
Program code ends up cached in RAM anyway. Shared libraries end up in shared memory anyway. You might want to rethink your strategy for improving performance.

/dev/shm is often used to explicitly create memory blocks for processes to share between them but in the end is just a ramdisk, no more, no less.
Login or Register to Ask a Question

Previous Thread | Next Thread

9 More Discussions You Might Find Interesting

1. Programming

Linux Shell Piping w/Shared Memory

So I am pretty new to the linux environment, and I am trying to create a shell that uses multiple pipes, and I read online that piping using shared memory space is more efficient than using regular piping. However, I have zero clue how to use shared memory space with pipes. Has anyone done this... (1 Reply)
Discussion started by: Greg_MC
1 Replies

2. Programming

Shared library with acces to shared memory.

Hello. I am new to this forum and I would like to ask for advice about low level POSIX programming. I have to implement a POSIX compliant C shared library. A file will have some variables and the shared library will have some functions which need those variables. There is one special... (5 Replies)
Discussion started by: iamjag
5 Replies

3. Red Hat

Unable to remove shared memory in Redhat Linux

unable to remove shared memory using ipcrm -m in linux $ ipcs -m ------ Shared Memory Segments -------- key shmid owner perms bytes nattch status 0x00000000 32768 root 644 80 2 0x00000000 65537 root ... (4 Replies)
Discussion started by: LinuxLearner
4 Replies

4. Red Hat

about shared memory space in Linux !

Dear Friends , I am confused about shared memory in Linux . plz look @ the below output : $ df -h Filesystem Size Used Avail Use% Mounted on /dev/sda1 126G 61G 59G 52% / tmpfs 1.7G 0 1.7G 0% /dev/shm Here , I see that every time... (1 Reply)
Discussion started by: shipon_97
1 Replies

5. UNIX for Advanced & Expert Users

Shared Memory

Hi, Using ipcs we can see shared memory, etc.. details. How can I add/remove shared memory(command name)? Thanks, Naga:cool: (2 Replies)
Discussion started by: Nagapandi
2 Replies

6. Programming

Shared memory for shared library

I am writing a shared library in Linux (but compatible with other UNIXes) and I want to allow multiple instances to share a piece of memory -- 1 byte is enough. What's the "best" way to do this? I want to optimize for speed and portability. Obviously, I'll have to worry about mutual exclusion. (0 Replies)
Discussion started by: otheus
0 Replies

7. Programming

Shared memory in shared library

I need to create a shared library to access an in memory DB. The DB is not huge, but big enough to make it cumbersome to carry around in every single process using the shared library. Luckily, it is pretty static information, so I don't need to worry much about synchronizing the data between... (12 Replies)
Discussion started by: DreamWarrior
12 Replies

8. Programming

memory sharing - not shared memory -

hi, this is the problem: i want to swap a linked list between 4 processes (unrelated), is there any way i can do that just by sending a pointer to a structure? //example typedef struct node { int x; char c; struct node *next; } node; or i should send the items ( x,c ) by... (9 Replies)
Discussion started by: elzalem
9 Replies

9. UNIX for Advanced & Expert Users

Shared memory shortage but lots of unused memory

I am running HP-UX B.11.11. I'm increasing a parameter for a database engine so that it uses more memory to buffer the disk drive (to speed up performance). I have over 5GB of memory not being used. But when I try to start the DB with the increased buffer parameter I get told. "Not... (1 Reply)
Discussion started by: cjcamaro
1 Replies
Login or Register to Ask a Question