what is the use of df , du , ulimit command in unix?

 The df , du , ulimt command is used by the super user (owner) to scan the disk , locate unwanted files and to remove files.

df (disk-free)

used to find amount of space used  by files and free space available. The df command shows the following information in 4 columns in unix and 6 columns in linux.

df options:

• -h : shows data in large unit blocks  ( GB , MB )
• -k : shows data in 1kb-blocks
• -m : shows data in 1mb-blocks

du (disk-usage)

used to find amount of space used  by sub-directories and files under the current directories. It descends all sub-directoriers from the directory in which the command is given,reporting the size of their contents.

df options:

• -h : shows data in large unit blocks  ( GB , MB )
• -k : shows data in 1kb-blocks
• -m : shows data in 1mb-blocks

ulimit(user limit)

used to limit the use of disk space by the user. This command is built-in in all shells. An ordinary user can not increase the limit can decrease the limit . Once the limit has been reduced it remains same until user log-outs.Therefore change will be only effective in current session. The system returns to default value , when the user logs-out.The limit can be only increased by the super user.

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