#inode

The file system’s inode (index node) contains one inode for each file residing in the file system. An inode stores essential information, including:o  File Type: Indicates if the entry is a regular file, directory, character device, or symbolic link.o  File Size: Represents the size of the file in bytes.o  Permissions: Specifies the read, write, and execute permissions for different…

df

To check inode

In the course of debugging a script it managed to touch a file which it named as "$HOME" in my cwd. EDIT: it turned out that it was ansible itself that was creating this directory. Obviously as this is a reserved name it caused no end of trouble in that I needed to be very careful in removing it.

In this case I can simply escape the dollar and remove it, but things are not always so easy:

[root@934eb43d0165 /]# echo rubbish > \$HOME [root@934eb43d0165 /]# rm -i \$HOME rm: remove regular file '$HOME'? n

Due to the difficulty of quoting this file and not having it expand to my actual homedir it is safer to just operate on the inode instead of the name.

the inode contains all the information about a file--indeed, it is not incorrect to say that the inode _is_ the file. -- from "info rm"

So, first of all ensure that this really is a different thing from my homedir and then remove it.

[root@934eb43d0165 /]# ls -il | grep HOME 137468 -rw-r--r--. 1 root root 8 Mar 2 20:03 $HOME

Background

We sometimes see an error “No space left on device”, 

# touch /tmp/testfile.txt

unable to create `/tmp/testfile.txt': No space left on device

but when we do a df -h, we will see that there is space on the disk. Eg, 

# df -h / Filesystem           Size  Used Avail Use% Mounted on /dev/sda2  9.5G  1.9G  7.7G  20% /

Reason

This occurs because the disk drive has no more free “inodes” . In simple terms, inodes are the “metadata” for files written on the disk. Consider this like a database which stores all the “information” about a file on the disk which is used to refer the file on the disk. 

A certain (small) percentage of the disk space is reserved to store this inode database for the filesystem written on the disk. As and when files are created on the disk, their corresponding inode information is also creates on the space reserved for the inode. 

The command df -i shows the inode information for that file system. Eg, to see the free inodes for / :: 

# df -i / Filesystem           Inodes IUsed   IFree IUse% Mounted on /dev/sda2 9961472 37264 9924208    1% /

On the system which is 100% full on the inodes, the output of df -i would look something like this :: 

# df -i / Filesystem           Inodes IUsed   IFree IUse% Mounted on /dev/sda2 9961472 9961472 0    100% /

Solution

There is (unfortunately) no way to dynamically add more inode space on the filesystem after it is created. So to recover from the current solution, the only way to delete some files from the disk until it free’s up some inode space on the disk for you to be able to add more files to the disk. 

Long term solution

While creating the filesystem, plan to allocate more inode space on the disk than the default allocated inodes on that file system. This can be done using the -i when creating the filesystem. The bigger the number, the less the number of inodes you will have. 

Also, it is always a best practice to create and manage filesystems using LVM (Linux Volume Manager) . LVM allows dynamic expansion of filesystems but adding more disk space to it and add more space to the disk also add more inodes to the file system.

More info can be found here

Ref Links for more information

No space left on device

What is an inode