free command : it is used to display amount of free and used memory in the system. it displays the total amount of free and used physical and swap memory in the system, as well as the buffers and caches used by the kernel. output will display total, used, free, shared, buffers, cache, buff/cache, available columns. for more information use man free or info free commands.
- total : Total installed memory (MemTotal and SwapTotal)
- used : Used memory (calculated as total - free - buffers - cache)
- free : Unused memory (MemFree and SwapFree)
- shared : Memory used (mostly) by tmpfs.
- buffers : Memory used by kernel buffers (Buffers)
- cache : Memory used by the page cache and slab
- buff/cache : Sum of buffers and cache
- available : Estimation of how much memory is available for starting new applications, without swapping.
following are options for
|-b or --bytes||display memory in bytes|
|-k or --kibi||display memory in kibibytes. this is by default|
|-m or --mebi||display memory in mebibytes|
|-g or --gibi||display memory in gibibytes|
|-h or --human||display memory in human readable format|
|-w or --wide||switch to the wide mode. In this mode buffers and cache are reported in two separate columns|
|-c or --count count||display the result count times. Requires the -s option|
|-l or --lohi||show detailed low and high memory statistics|
|-s or --seconds delay||continuously display the result delay seconds apart|
|--si||Use kilo, mega, giga etc (power of 1000) instead of kibi, mebi, gibi (power of 1024).|
|-t or --total||display a line showing the column totals|
df command : it is used to report file system disk space usage.df displays the amount of disk space available on the file system containing each file name argument. If no file name is given, then it print space available on all currently mounted file systems. by default Disk space is given in 1K blocks. for more information use man df or info df commands.
df options files
following table shows option for
|-a or --all||include pseudo, duplicate, inaccessible file systems|
|-h or --human-readable||print sizes in human readable format (powers of 1024)|
|-H or --si||print sizes in powers of 1000|
|-i or --inodes||list inode information instead of block usage|
|-l, --local||limit listing to local file systems|
|--no-sync||this is by default. do not invoke sync before getting usage info|
|-P or --portability||use the POSIX output format|
|--sync||invoke sync before getting usage info|
|--total||elide all entries insignificant to available space, and produce a grand total|
|-t or --type=TYPE||limit listing to file systems of type TYPE|
|-T or --print-type||print file system type|
|-x or --exclude-type=TYPE||limit listing to file systems not of type TYPE|
watch command : it is used to execute a command or program periodically and print output in full screen. it allows to watch output changing over time. at the top of full screen(right hand side) it will display the interval, command, and current time. by default command or program will run periodically in every 2 seconds. to close or exit the output use shortcut. ctrl + c
watch option command or program
in following Example we keep watch on
free command. it will run periodically in every 2 seconds. so any change in memory will be visible on screen.
following table shows options for
|-b or --beep||beep if command has a non-zero exit|
|-d or --differences||highlight the changes when any change happen in output.|
|-e or --errexit||freeze updates on command error and exit after a key press|
|-g or --chgexit||exit when the output of command changes|
|-n N or --interval N|| specify interval to update or periodically run command or program.
here N is seconds
|-t or --no-title|| turn off the header showing the interval, command, and current time at the
top of the display, as well as the following blank line
in following examples we set watch on ls command. this will allow us to see any updates in file operations like new file created, new sub directory created, deletion of file or directory.