Command to know the Available Memory on Linux System

To know the total Memory available on a Linux System you can take a look into /proc/meminfo file.

root@ubuntu # cat /proc/meminfo 
MemTotal:        4026792 kB
MemFree:         2559056 kB
MemAvailable:    3236968 kB
Buffers:           39764 kB
Cached:          1061340 kB
SwapCached:            0 kB
Active:           356600 kB
Inactive:         905332 kB
Active(anon):      79516 kB
Inactive(anon):   411764 kB
Active(file):     277084 kB
Inactive(file):   493568 kB
Unevictable:           0 kB
Mlocked:               0 kB
SwapTotal:       1048572 kB
SwapFree:        1048572 kB
Dirty:                 8 kB
Writeback:             0 kB
AnonPages:        159336 kB
Mapped:           218656 kB
Shmem:            330452 kB
KReclaimable:      69836 kB
...
Hugetlb:               0 kB

The value next MemTotal is the total memory (RAM) you have on the System in Kb.

You can also make use of the free command to know the memory details,

root@linux # free -k
               total        used        free      shared  buff/cache   available
Mem:         4026792      294548     2561276      330452     1170968     3239216
Swap:        1048572           0     1048572

root@linux:/# free -m
               total        used        free      shared  buff/cache   available
Mem:            3932         289        2499         322        1143        3161
Swap:           1023           0        1023

root@ linux:/# free -g
               total        used        free      shared  buff/cache   available
Mem:               3           0           2           0           1           3
Swap:              0           0           0