CentOS default installation gave about 60% of memory space to the tmpfs partition - Is this an issue?

Question

I installed a CentOS server which will be used for xen hypervisor. The server has two Intel(R) Xeon(R) CPU E5620 and 148G memory. The OS was installed on a 120G SSD drive. After the installation, I found that the tmpfs partition occupied about 60% of the drive. Even though I don't need much space for the OS, will there be any problem with 71G tmp partition? Thanks for any comment.

[root@cloud ~]# df -h
Filesystem            Size  Used Avail Use% Mounted on 
/dev/mapper/VolGroup00-LogVol00
                       55G  1.1G   51G   3% /
/dev/sda1              99M   13M   82M  14% /boot
tmpfs                  71G     0   71G   0% /dev/shm

EDIT:

[root@cloud ~]# fdisk -l

Disk /dev/sda: 120.0 GB, 120034123776 bytes
255 heads, 63 sectors/track, 14593 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

    Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1          13      104391   83  Linux
/dev/sda2              14       14593   117113850   8e  Linux LVM

[root@cloud ~]# vgdisplay
  --- Volume group ---
  VG Name               VolGroup00
  System ID
  Format                lvm2
  Metadata Areas        1
  Metadata Sequence No  3
  VG Access             read/write
  VG Status             resizable
  MAX LV                0
  Cur LV                2
  Open LV               2
  Max PV                0
  Cur PV                1
  Act PV                1
  VG Size               111.69 GB
  PE Size               32.00 MB
  Total PE              3574
  Alloc PE / Size       3573 / 111.66 GB
  Free  PE / Size       1 / 32.00 MB
  VG UUID               37dcLa-zJv6-i2j3-3Xvk-keXO-HJDh-UDgQ8l

  [root@cloud ~]# lvdisplay
    --- Logical volume ---
    LV Name                /dev/VolGroup00/LogVol00
    VG Name                VolGroup00
    LV UUID                Kj5LoJ-kCOq-MWhV-Wc3s-kds1-AsNE-cs9Ibh
    LV Write Access        read/write
    LV Status              available
    # open                 1
    LV Size                56.50 GB
    Current LE             1808
    Segments               1
    Allocation             inherit
    Read ahead sectors     auto
    - currently set to     256
    Block device           253:0

    --- Logical volume ---
    LV Name                /dev/VolGroup00/LogVol01
    VG Name                VolGroup00
    LV UUID                4h7uvI-as7G-OTWE-ufea-CqqO-ws76-WolJCt
    LV Write Access        read/write
    LV Status              available
    # open                 1
    LV Size                55.16 GB
    Current LE             1765
    Segments               1
    Allocation             inherit
    Read ahead sectors     auto
    - currently set to     256
    Block device           253:1

Update your question with the output of `fdisk -l`, and `vgdisplay`. — Zoredache, Nov 16 '11 at 17:54
Your vgdisplay output shows that you have 2 logical volumes, but your df output shows only one LV as being mounted (assuming you pasted the full output). Since all your space is from the VG is used, my guess is that the space your missing is in that other logical volume. Run `lvdisplay` to see a list of your logical volumes, and how much space is allocated to each. — Zoredache, Nov 16 '11 at 18:15
I just add the lvdisplay output. It shows I have two logical volumes, each use about 56G. — garconcn, Nov 16 '11 at 18:48

ewwhite · Accepted Answer · 2011-11-16T18:14:11.977

4

The tmpfs partition you see listed is the /dev/shm shared memory "ramdisk". It's equal to 50% of your physical RAM by default. This is unrelated to your OS drive (/dev/mapper/VolGroup00-LogVol00) mounted at /. So there's nothing to worry about here. Your system drive is 55G at present, and you're only using 1.1G of it.

See a thorough description at: http://www.cyberciti.biz/tips/what-is-devshm-and-its-practical-usage.html

edited Nov 16 '11 at 18:14

answered Nov 16 '11 at 17:55

ewwhite

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Thanks for the link. I had read thorough it and the comments. I am wondering is the ramdisk on Linux different from Windows? On Windows, if I create a ramdisk, it actually use the RAM space. But here it seems the ramdisk use the disk space. – garconcn Nov 16 '11 at 18:26
1

Here, it's dynamic. The space is available, but isn't used unless you place files in /dev/shm. It is NOT persistent across reboots. – ewwhite Nov 16 '11 at 18:27

score 0 · Answer 2 · answered Nov 16 '11 at 21:14

I would not recommend to use that much memory for /dev/shm on a Dom0.

You have two options:

Limit the size of /dev/shm with the according mount-option (e.g. to 1 GB)
Limit the memory available for the Dom0 (e.g. to 2 GB RAM).

The latter is recommended by SuSE. The default for /dev/shm is halv of the available RAM - which can get you into trouble on a machine which uses lots of RAM (like a Dom0).

CentOS default installation gave about 60% of memory space to the tmpfs partition - Is this an issue?

2 Answers2