we often df–th check the disk capacity in daily operation, so what is the role of /dev/shm ?
$ df-th
File system type capacity used available % mount point
/dev/sda2 ext3 57G 32G 23G 59%/
/dev/sda5 ext3 476G 341G 111G 76%/var
/dev/sda1 ext3 190M 29M 153M 16%/boot
/dev/sdb1 ext2 1.8T 1.2T 584G 67%/ext
tmpfs tmpfs 20G 9.5G 11G 49%/dev/shm
The /dev/shm is in memory, not on disk. Because the /dev/shm exists in memory, the speed is definitely better than the disk.
/dev/shm is not an immediate use of memory, but rather a method of consuming memory if needed. In the above example, the value of the/dev/shm setting is 20G, and we see that the data that has been written to 9.5G is used to consume 9.5G of memory.
The /dev/shm uses the tmpfs file system, which has the following advantages :
1. fast speed.
2. Dynamic allocation: Write more data,/dev/shm occupy more memory, delete data in /dev/shm , then reduce memory consumption. Not so good for the full use of memory.
/dev/shm Another feature: After the system restarts and after /dev/shm is mounted, the data in the/dev/shm disappears.
/DEV/SHM The default value is half of memory, and sometimes increases /dev/shmas needed, such as the value in the set memory_target in Oracle exceeds the The size of the /dev/shm .
To Modify the /dev/shm size:
1.vim/etc/fstab
The original is this:
tmpfs/dev/shm tmpfs defaults 0 0
modified as follows, that is, 20G
tmpfs/dev/shm tmpfs defaults, size=20000m 0 0
2. effective after re- Mount/dev/shm
# Mount-o Remount/dev/shm
or umount/dev/shm .
Mount/dev/shm
See if it takes effect with df–th
You can also use the following method
# mkdir/mnt/tmp
# mount-t Tmpfs-o size=256m,mode=1777 tmpfs/mnt/tmp
Problem Solving:
Sometimes you may encounter a situation where /dev/shm cannot unload
# UMOUNT/DEV/SHM
umount:/dev/shm:device is busy.
treated with fuser
# FUSER-KM/DEV/SHM
# UMOUNT/DEV/SHM
# MOUNT/DEV/SHM
fuser Command
-k:kill processes accessing the named file (kills all processes that are accessing the specified file
)
- m indicates the file system or block device (in Mount state) where the specified file resides. All processes that access the file system are listed.
First, create a TMP folder in/dev/shm and then bind to the actual/tmp
#mkdir/dev/shm/tmp
#chmod 1777/dev/shm/tmp
#mount –bind/dev/shm/tmp/tmp (–bind)
The Linux/dev/shm directory is used to optimize