I'm typing a shell script to find out the total physical memory in some RHEL linux boxes.
First of all I want to stress that I'm interested in the total physical memory recognized by kernel, not just the available memory. Therefore, please, avoid answers suggesting to read /proc/meminfo or to use the free, top or sar commands -- In all these cases, their "total memory" values mean "available memory" ones.
The first thought was to read the boot kernel messages:
Memory: 61861540k/63438844k available (2577k kernel code, 1042516k reserved, 1305k data, 212k init)
But in some linux boxes, due to the use of EMC2's PowerPath software and its flooding boot messages in the kernel startup, that useful boot kernel message is not available, not even in the /var/log/dmesg file.
The second option was the dmidecode command (I'm warned against the possible mismatch of kernel recognized RAM and real RAM due to the limitations of some older kernels and architectures). The option --memory simplifies the script but I realized that older releases of that command has no --memory option.
My last chance was the getconf command. It reports the memory page size, but not the total number of physical pages -- the _PHYS_PAGES system variable seems to be the available physical pages, not the total physical pages.
# getconf -a | grep PAGES PAGESIZE 4096 _AVPHYS_PAGES 1049978 _PHYS_PAGES 15466409
My question: Is there another way to get the total amount of physical memory, suitable to be parsed by a shell script?
If you're interested in the physical RAM, use the command dmidecode. It gives you a lot more information than just that, but depending on your use case, you might also want to know if the 8G in the system come from 2x4GB sticks or 4x2GB sticks.
Have you tried cat /proc/meminfo? You can then grep out what you want, MemTotal e.g.
Updated Example (btw. thanks, Masta):
awk '/MemTotal/ {print $2}' /proc/meminfo
cat /proc/meminfo | grep MemTotal or free gives you the exact amount of RAM your server has. This is not "available memory".
I guess your issue comes up when you have a VM and you would like to calculate the full amount of memory hosted by the hypervisor but you will have to log into the hypervisor in that case.
cat /proc/meminfo | grep MemTotal
is equivalent to
getconf -a | grep PAGES | awk 'BEGIN {total = 1} {if (NR == 1 || NR == 3) total *=$NF} END {print total / 1024" kB"}'
One more useful command:vmstat -s | grep memory
sample output on my machine is:
2050060 K total memory
1092992 K used memory
743072 K active memory
177084 K inactive memory
957068 K free memory
385388 K buffer memory
another useful command to get memory information is:free
sample output is:
total used free shared buffers cached
Mem: 2050060 1093324 956736 108 385392 386812
-/+ buffers/cache: 321120 1728940
Swap: 2095100 2732 2092368
One observation here is that, the command free gives information about swap space also.
The following link may be useful for you:
http://www.linuxnix.com/find-ram-details-in-linuxunix/
Add the last 2 entries of /proc/meminfo, they give you the exact memory present on the host.
Example:
DirectMap4k: 10240 kB
DirectMap2M: 4184064 kB
10240 + 4184064 = 4194304 kB = 4096 MB.
free -h | awk '/Mem\:/ { print $2 }'
This will provide you with the total memory in your system in human readable format and automatically scale to the appropriate unit ( e.g. bytes, KB, MB, or GB).
dmidecode -t 17 | grep Size:
Adding all above values displayed after "Size: " will give exact total physical size of all RAM sticks in server.
Total memory in Mb:
x=$(awk '/MemTotal/ {print $2}' /proc/meminfo)
echo $((x/1024))
or:
x=$(awk '/MemTotal/ {print $2}' /proc/meminfo) ; echo $((x/1024))
These are the ways :
1. /proc/meminfo
MemTotal: 8152200 kB
MemFree: 760808 kB
You can write a code or script to parse it.
2. Use sysconf by using below macros
sysconf (_SC_PHYS_PAGES) * sysconf (_SC_PAGESIZE);
3. By using sysinfo system call
int sysinfo(struct sysinfo *info);
struct sysinfo { .
.
unsigned long totalram; /*Total memory size to use */
unsigned long freeram; /* Available memory size*/
.
.
};
Total online memory
Calculate the total online memory using the sys-fs.
totalmem=0;
for mem in /sys/devices/system/memory/memory*; do
[[ "$(cat ${mem}/online)" == "1" ]] \
&& totalmem=$((totalmem+$((0x$(cat /sys/devices/system/memory/block_size_bytes)))));
done
#one-line code
totalmem=0; for mem in /sys/devices/system/memory/memory*; do [[ "$(cat ${mem}/online)" == "1" ]] && totalmem=$((totalmem+$((0x$(cat /sys/devices/system/memory/block_size_bytes))))); done
echo ${totalmem} bytes
echo $((totalmem/1024**3)) GB
Example output for 4 GB system:
4294967296 bytes
4 GB
Explanation
/sys/devices/system/memory/block_size_bytes
Number of bytes in a memory block (hex value). Using 0x in front of the value makes sure it's properly handled during the calculation.
/sys/devices/system/memory/memory*
Iterating over all available memory blocks to verify they are online and add the calculated block size to totalmem if they are.
[[ "$(cat ${mem}/online)" == "1" ]] &&
You can change or remove this if you prefer another memory state.
I find htop a useful tool.
sudo apt-get install htop
and then
free -m
will give the information you need.
来源：https://stackoverflow.com/questions/20348007/how-can-i-find-out-the-total-physical-memory-ram-of-my-linux-box-suitable-to-b