I used the free -h command to show the available RAM in the live image of Lubuntu loaded into RAM .
If I created it by the command: dd if=lubuntu-19.04-desktop-amd64.iso of=/dev/sdb bs=512k, then I get my actual total ram.
But if I created the live-usb using MKusb, I get about 1gb less of ram ... I'm using Mkusb to make a persistent live usb.
As noted in comments, 19.04 has passed the end of life date, so I think we should test not only that version but also another version (that is still supported).
Cloned USB boot drives made with dd, mkusb and any other cloning tool will be identical. If there is a difference, it is not a cloning tool, or there is some write error (maybe due to faulty hardware). The block size selected by dd with bs can change the speed of cloning, but does not change the result of the cloning.
According to my experience, Ubuntu live (live-only) systems allocate approximately half of the available RAM to the root file system /
A persistent live drive made with mkusb version 12 alias mkusb-dus uses an overlay method, where the size of the partition for persistence decides the size of the root file system.
So when the partition for persistence is
greater than half of the RAM, the root file system will increase compared to a live system,
smaller than half of the RAM, the root file system will decrease compared to a live system.
The amount of RAM for other purposes (which is free before it is used by the programs, that you start) will depend on how much that is used for the overlay system. The following test results describe what happens in different cases.
I found no unexpected behaviour when testing Lubuntu 19.04. For that reason I am rather sure that those results can also represent Lubuntu 18.04.x LTS.
I also tested Lubuntu 19.10, which has a modified mechanism in the package casper, and can be expected to behave in a different way. These results should also represent Focal Fossa to be released as Lubuntu 20.04 LTS.
Summary
The main difference is the free memory in case #3 in both versions (19.04 and 19.10), and the reason is that the boot option toram was used in that case. It means that the [whole] image of the iso file is copied to RAM. Otherwise there is no significant difference in the usage of RAM.
Details
Explanation of the list above:
a persistent live drive made with mkusb (and 67% selected for persistence)
the remaining part of the list is output from free -h
Shellscript
The following shellscript was used to collect data from each of the run case.
echo "lsb_release -a ########################################" >> /media/lubuntu/KEEP_ME/result.txt
lsb_release -a >> /media/lubuntu/KEEP_ME/result.txt
echo "cat /proc/cmdline ##########" >> /media/lubuntu/KEEP_ME/result.txt
cat /proc/cmdline >> /media/lubuntu/KEEP_ME/result.txt
echo "sudo lsblk -o name,fstype,label,mountpoint,size,model ##########" >> /media/lubuntu/KEEP_ME/result.txt
sudo lsblk -o name,fstype,label,mountpoint,size,model >> /media/lubuntu/KEEP_ME/result.txt
echo "df -h ##########" >> /media/lubuntu/KEEP_ME/result.txt
df -h >> /media/lubuntu/KEEP_ME/result.txt
echo "free -h ##########" >> /media/lubuntu/KEEP_ME/result.txt
free -h >> /media/lubuntu/KEEP_ME/result.txt
The following output lists can be used by you, if you want to compare your results with mine in order to discuss differences.
Output for Lubuntu 19.04
lsb_release -a ########################################
Distributor ID: Ubuntu
Description: Ubuntu 19.04
Release: 19.04
Codename: disco
cat /proc/cmdline ##########
file=/cdrom/preseed/lubuntu.seed boot=casper initrd=/casper/initrd quiet splash --- debian-installer/language=sv keyboard-configuration/layoutcode?=se
sudo lsblk -o name,fstype,label,mountpoint,size,model ##########
NAME FSTYPE LABEL MOUNTPOINT SIZE MODEL
loop0 squashfs /rofs 1,5G
sda iso9660 Lubuntu 19.04 amd64 /cdrom 14,8G SS3
├─sda1 iso9660 Lubuntu 19.04 amd64 1,6G
└─sda2 vfat Lubuntu 19.04 amd64 3,7M
sdb 15G Transcend_16GB
└─sdb1 vfat KEEP_ME /media/lubuntu/KEEP_ME 15G
sr0 1024M TSSTcorp_CDDVDW_SN-208AB
sr1 11M AutoRun_Disk
zram0 [SWAP] 478,2M
zram1 [SWAP] 478,2M
zram2 [SWAP] 478,2M
zram3 [SWAP] 478,2M
df -h ##########
Filesystem Size Used Avail Use% Mounted on
udev 1,9G 0 1,9G 0% /dev
tmpfs 383M 1,4M 382M 1% /run
/dev/sda 1,6G 1,6G 0 100% /cdrom
/dev/loop0 1,5G 1,5G 0 100% /rofs
/cow 1,9G 32M 1,9G 2% /
tmpfs 1,9G 6,3M 1,9G 1% /dev/shm
tmpfs 5,0M 4,0K 5,0M 1% /run/lock
tmpfs 1,9G 0 1,9G 0% /sys/fs/cgroup
tmpfs 1,9G 0 1,9G 0% /tmp
tmpfs 383M 8,0K 383M 1% /run/user/999
/dev/sdb1 15G 3,4G 12G 23% /media/lubuntu/KEEP_ME
free -h ##########
total used free shared buff/cache available
Mem: 3,7Gi 339Mi 2,7Gi 63Mi 742Mi 3,1Gi
Swap: 1,9Gi 0B 1,9Gi
lsb_release -a ########################################
Distributor ID: Ubuntu
Description: Ubuntu 19.04
Release: 19.04
Codename: disco
cat /proc/cmdline ##########
BOOT_IMAGE=(hd0,gpt4)/casper/vmlinuz file=/cdrom/preseed/lubuntu.seed boot=casper quiet splash persistent ---
sudo lsblk -o name,fstype,label,mountpoint,size,model ##########
NAME FSTYPE LABEL MOUNTPOINT SIZE MODEL
loop0 squashfs /rofs 1.5G
sda 14.6G Extreme
├─sda1 ntfs usbdata /media/lubuntu/usbdata 4.2G
├─sda2 1M
├─sda3 vfat usbboot 244M
├─sda4 iso9660 Lubuntu 19.04 amd64 /cdrom 1.6G
└─sda5 ext4 casper-rw /media/lubuntu/casper-rw 8.6G
sdb 15G Transcend_16GB
└─sdb1 vfat KEEP_ME /media/lubuntu/KEEP_ME 15G
sr0 1024M TSSTcorp_CDDVDW_SN-208AB
sr1 11M AutoRun_Disk
zram0 [SWAP] 478.2M
zram1 [SWAP] 478.2M
zram2 [SWAP] 478.2M
zram3 [SWAP] 478.2M
df -h ##########
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 0 1.9G 0% /dev
tmpfs 383M 1.4M 382M 1% /run
/dev/sda4 1.6G 1.6G 0 100% /cdrom
/dev/loop0 1.5G 1.5G 0 100% /rofs
/cow 8.5G 61M 8.0G 1% /
tmpfs 1.9G 6.3M 1.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
tmpfs 1.9G 0 1.9G 0% /tmp
tmpfs 383M 8.0K 383M 1% /run/user/999
/dev/sdb1 15G 3.4G 12G 23% /media/lubuntu/KEEP_ME
/dev/sda5 8.5G 61M 8.0G 1% /media/lubuntu/casper-rw
/dev/sda1 4.3G 23M 4.3G 1% /media/lubuntu/usbdata
free -h ##########
total used free shared buff/cache available
Mem: 3.7Gi 344Mi 2.7Gi 31Mi 710Mi 3.1Gi
Swap: 1.9Gi 0B 1.9Gi
lsb_release -a ########################################
Distributor ID: Ubuntu
Description: Ubuntu 19.04
Release: 19.04
Codename: disco
cat /proc/cmdline ##########
BOOT_IMAGE=(hd0,gpt4)/casper/vmlinuz file=/cdrom/preseed/lubuntu.seed boot=casper quiet splash toram nopersistent ---
sudo lsblk -o name,fstype,label,mountpoint,size,model ##########
NAME FSTYPE LABEL MOUNTPOINT SIZE MODEL
loop0 squashfs /rofs 1.5G
sda 14.6G Extreme
├─sda1 ntfs usbdata /media/lubuntu/usbdata 4.2G
├─sda2 1M
├─sda3 vfat usbboot 244M
├─sda4 iso9660 Lubuntu 19.04 amd64 /media/lubuntu/Lubuntu 19.04 amd64 1.6G
└─sda5 ext4 casper-rw /media/lubuntu/casper-rw 8.6G
sdb 15G Transcend_16GB
└─sdb1 vfat KEEP_ME /media/lubuntu/KEEP_ME 15G
sr0 1024M TSSTcorp_CDDVDW_SN-208AB
sr1 11M AutoRun_Disk
zram0 [SWAP] 478.2M
zram1 [SWAP] 478.2M
zram2 [SWAP] 478.2M
zram3 [SWAP] 478.2M
df -h ##########
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 0 1.9G 0% /dev
tmpfs 383M 1.4M 382M 1% /run
/dev/shm 1.7G 1.6G 79M 96% /cdrom
/dev/loop0 1.5G 1.5G 0 100% /rofs
/cow 1.9G 26M 1.9G 2% /
tmpfs 1.9G 6.3M 1.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
tmpfs 1.9G 0 1.9G 0% /tmp
tmpfs 383M 8.0K 383M 1% /run/user/999
/dev/sdb1 15G 3.4G 12G 23% /media/lubuntu/KEEP_ME
/dev/sda5 8.5G 75M 8.0G 1% /media/lubuntu/casper-rw
/dev/sda4 1.6G 1.6G 0 100% /media/lubuntu/Lubuntu 19.04 amd64
/dev/sda1 4.3G 23M 4.3G 1% /media/lubuntu/usbdata
free -h ##########
total used free shared buff/cache available
Mem: 3.7Gi 344Mi 1.3Gi 1.6Gi 2.1Gi 1.6Gi
Swap: 1.9Gi 0B 1.9Gi
lsb_release -a ########################################
Distributor ID: Ubuntu
Description: Ubuntu 19.04
Release: 19.04
Codename: disco
cat /proc/cmdline ##########
BOOT_IMAGE=(hd0,gpt4)/casper/vmlinuz file=/cdrom/preseed/lubuntu.seed boot=casper quiet splash ---
sudo lsblk -o name,fstype,label,mountpoint,size,model ##########
NAME FSTYPE LABEL MOUNTPOINT SIZE MODEL
loop0 squashfs /rofs 1.5G
sda 14.6G Extreme
├─sda1 ntfs usbdata /media/lubuntu/usbdata 4.2G
├─sda2 1M
├─sda3 vfat usbboot 244M
├─sda4 iso9660 Lubuntu 19.04 amd64 /cdrom 1.6G
└─sda5 ext4 casper-rw /media/lubuntu/casper-rw 8.6G
sdb 15G Transcend_16GB
└─sdb1 vfat KEEP_ME /media/lubuntu/KEEP_ME 15G
sr0 1024M TSSTcorp_CDDVDW_SN-208AB
sr1 11M AutoRun_Disk
zram0 [SWAP] 478.2M
zram1 [SWAP] 478.2M
zram2 [SWAP] 478.2M
zram3 [SWAP] 478.2M
df -h ##########
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 0 1.9G 0% /dev
tmpfs 383M 1.4M 382M 1% /run
/dev/sda4 1.6G 1.6G 0 100% /cdrom
/dev/loop0 1.5G 1.5G 0 100% /rofs
/cow 1.9G 24M 1.9G 2% /
tmpfs 1.9G 6.3M 1.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
tmpfs 1.9G 0 1.9G 0% /tmp
tmpfs 383M 8.0K 383M 1% /run/user/999
/dev/sdb1 15G 3.4G 12G 23% /media/lubuntu/KEEP_ME
/dev/sda5 8.5G 75M 8.0G 1% /media/lubuntu/casper-rw
/dev/sda1 4.3G 23M 4.3G 1% /media/lubuntu/usbdata
free -h ##########
total used free shared buff/cache available
Mem: 3.7Gi 344Mi 2.7Gi 54Mi 719Mi 3.1Gi
Swap: 1.9Gi 0B 1.9Gi
Output for Lubuntu 19.10
lsb_release -a ########################################
Distributor ID: Ubuntu
Description: Ubuntu 19.10
Release: 19.10
Codename: eoan
cat /proc/cmdline ##########
file=/cdrom/preseed/lubuntu.seed initrd=/casper/initrd quiet splash ---
sudo lsblk -o name,fstype,label,mountpoint,size,model ##########
NAME FSTYPE LABEL MOUNTPOINT SIZE MODEL
loop0 squashfs /rofs 1.5G
sdb iso9660 Lubuntu 19.10 amd64 14.8G SS3
├─sdb1 iso9660 Lubuntu 19.10 amd64 /cdrom 1.6G
├─sdb2 vfat Lubuntu 19.10 amd64 3.9M
└─sdb3 ext4 casper-rw /var/crash 13.2G
sdc 15G Transcend_16GB
└─sdc1 vfat KEEP_ME /media/lubuntu/KEEP_ME 15G
sr0 1024M TSSTcorp_CDDVDW_SN-208AB
sr1 11M AutoRun_Disk
zram0 [SWAP] 477.3M
zram1 [SWAP] 477.3M
zram2 [SWAP] 477.3M
zram3 [SWAP] 477.3M
df -h ##########
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 0 1.9G 0% /dev
tmpfs 382M 6.2M 376M 2% /run
/dev/sdb1 1.6G 1.6G 0 100% /cdrom
/dev/loop0 1.5G 1.5G 0 100% /rofs
/cow 1.9G 17M 1.9G 1% /
/dev/disk/by-label/casper-rw 13G 41M 13G 1% /var/log
tmpfs 1.9G 6.7M 1.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
tmpfs 1.9G 0 1.9G 0% /tmp
tmpfs 382M 8.0K 382M 1% /run/user/999
/dev/sdc1 15G 3.4G 12G 23% /media/lubuntu/KEEP_ME
free -h ##########
total used free shared buff/cache available
Mem: 3.7Gi 337Mi 2.7Gi 50Mi 745Mi 3.1Gi
Swap: 1.9Gi 0B 1.9Gi
lsb_release -a ########################################
Distributor ID: Ubuntu
Description: Ubuntu 19.10
Release: 19.10
Codename: eoan
cat /proc/cmdline ##########
BOOT_IMAGE=(hd0,gpt4)/casper/vmlinuz file=/cdrom/preseed/lubuntu.seed quiet splash persistent ---
sudo lsblk -o name,fstype,label,mountpoint,size,model ##########
NAME FSTYPE LABEL MOUNTPOINT SIZE MODEL
loop0 squashfs /rofs 1.5G
sdb 14.6G Extreme
├─sdb1 ntfs usbdata /media/lubuntu/usbdata 4.2G
├─sdb2 1M
├─sdb3 vfat usbboot 244M
├─sdb4 iso9660 Lubuntu 19.10 amd64 /cdrom 1.6G
└─sdb5 ext4 casper-rw /media/lubuntu/casper-rw 8.6G
sdc 15G Transcend_16GB
└─sdc1 vfat KEEP_ME /media/lubuntu/KEEP_ME 15G
sr0 1024M TSSTcorp_CDDVDW_SN-208AB
sr1 11M AutoRun_Disk
zram0 [SWAP] 477.3M
zram1 [SWAP] 477.3M
zram2 [SWAP] 477.3M
zram3 [SWAP] 477.3M
df -h ##########
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 0 1.9G 0% /dev
tmpfs 382M 1.4M 381M 1% /run
/dev/sdb4 1.6G 1.6G 0 100% /cdrom
/dev/loop0 1.5G 1.5G 0 100% /rofs
/cow 8.5G 60M 8.0G 1% /
tmpfs 1.9G 6.3M 1.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
tmpfs 1.9G 0 1.9G 0% /tmp
tmpfs 382M 8.0K 382M 1% /run/user/999
/dev/sdc1 15G 3.4G 12G 23% /media/lubuntu/KEEP_ME
/dev/sdb5 8.5G 60M 8.0G 1% /media/lubuntu/casper-rw
/dev/sdb1 4.3G 23M 4.2G 1% /media/lubuntu/usbdata
free -h ##########
total used free shared buff/cache available
Mem: 3.7Gi 335Mi 2.7Gi 23Mi 733Mi 3.1Gi
Swap: 1.9Gi 0B 1.9Gi
lsb_release -a ########################################
Distributor ID: Ubuntu
Description: Ubuntu 19.10
Release: 19.10
Codename: eoan
cat /proc/cmdline ##########
BOOT_IMAGE=(hd0,gpt4)/casper/vmlinuz file=/cdrom/preseed/lubuntu.seed quiet splash toram nopersistent ---
sudo lsblk -o name,fstype,label,mountpoint,size,model ##########
NAME FSTYPE LABEL MOUNTPOINT SIZE MODEL
loop0 squashfs /rofs 1.5G
sdb 14.6G Extreme
├─sdb1 ntfs usbdata /media/lubuntu/usbdata 4.2G
├─sdb2 1M
├─sdb3 vfat usbboot 244M
├─sdb4 iso9660 Lubuntu 19.10 amd64 /media/lubuntu/Lubuntu 19.10 amd64 1.6G
└─sdb5 ext4 casper-rw /media/lubuntu/casper-rw 8.6G
sdc 15G Transcend_16GB
└─sdc1 vfat KEEP_ME /media/lubuntu/KEEP_ME 15G
sr0 1024M TSSTcorp_CDDVDW_SN-208AB
sr1 11M AutoRun_Disk
zram0 [SWAP] 477.3M
zram1 [SWAP] 477.3M
zram2 [SWAP] 477.3M
zram3 [SWAP] 477.3M
df -h ##########
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 0 1.9G 0% /dev
tmpfs 382M 1.4M 381M 1% /run
/dev/shm 1.7G 1.6G 80M 96% /cdrom
/dev/loop0 1.5G 1.5G 0 100% /rofs
/cow 1.9G 25M 1.9G 2% /
tmpfs 1.9G 6.3M 1.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
tmpfs 1.9G 0 1.9G 0% /tmp
tmpfs 382M 8.0K 382M 1% /run/user/999
/dev/sdc1 15G 3.4G 12G 23% /media/lubuntu/KEEP_ME
/dev/sdb5 8.5G 74M 8.0G 1% /media/lubuntu/casper-rw
/dev/sdb4 1.6G 1.6G 0 100% /media/lubuntu/Lubuntu 19.10 amd64
/dev/sdb1 4.3G 23M 4.2G 1% /media/lubuntu/usbdata
free -h ##########
total used free shared buff/cache available
Mem: 3.7Gi 339Mi 1.3Gi 1.6Gi 2.1Gi 1.6Gi
Swap: 1.9Gi 0B 1.9Gi
lsb_release -a ########################################
Distributor ID: Ubuntu
Description: Ubuntu 19.10
Release: 19.10
Codename: eoan
cat /proc/cmdline ##########
BOOT_IMAGE=(hd0,gpt4)/casper/vmlinuz file=/cdrom/preseed/lubuntu.seed quiet splash ---
sudo lsblk -o name,fstype,label,mountpoint,size,model ##########
NAME FSTYPE LABEL MOUNTPOINT SIZE MODEL
loop0 squashfs /rofs 1.5G
sdb 14.6G Extreme
├─sdb1 ntfs usbdata /media/lubuntu/usbdata 4.2G
├─sdb2 1M
├─sdb3 vfat usbboot 244M
├─sdb4 iso9660 Lubuntu 19.10 amd64 /cdrom 1.6G
└─sdb5 ext4 casper-rw /var/crash 8.6G
sdc 15G Transcend_16GB
└─sdc1 vfat KEEP_ME /media/lubuntu/KEEP_ME 15G
sr0 1024M TSSTcorp_CDDVDW_SN-208AB
sr1 11M AutoRun_Disk
zram0 [SWAP] 477.3M
zram1 [SWAP] 477.3M
zram2 [SWAP] 477.3M
zram3 [SWAP] 477.3M
df -h ##########
Filesystem Size Used Avail Use% Mounted on
udev 1.9G 0 1.9G 0% /dev
tmpfs 382M 6.2M 376M 2% /run
/dev/sdb4 1.6G 1.6G 0 100% /cdrom
/dev/loop0 1.5G 1.5G 0 100% /rofs
/cow 1.9G 17M 1.9G 1% /
/dev/disk/by-label/casper-rw 8.5G 74M 8.0G 1% /var/log
tmpfs 1.9G 6.3M 1.9G 1% /dev/shm
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 1.9G 0 1.9G 0% /sys/fs/cgroup
tmpfs 1.9G 0 1.9G 0% /tmp
tmpfs 382M 8.0K 382M 1% /run/user/999
/dev/sdc1 15G 3.4G 12G 23% /media/lubuntu/KEEP_ME
/dev/sdb1 4.3G 23M 4.2G 1% /media/lubuntu/usbdata
free -h ##########
total used free shared buff/cache available
Mem: 3.7Gi 340Mi 2.7Gi 45Mi 741Mi 3.1Gi
Swap: 1.9Gi 0B 1.9Gi
