The Linux/dev/shm directory is used to optimize

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