sudo dd if=/dev/zero of=/swapfile bs=1024 count=1024000;sudo mkswap /swapfile; sudo swapon /swapfile

create an emergency swapfile when the existing swap space is getting tight

Create a temporary file that acts as swap space. In this example it's a 1GB file at the root of the file system. This additional capacity is added to the existing swap space.
Sample Output
%free -tom
             total       used       free     shared    buffers     cached
Mem:          1010        997         12          0          1        395
Swap:         2047         43       2003
Total:        3057       1041       2016

%sudo dd if=/dev/zero of=/swapfile bs=1024 count=1024000;sudo mkswap /swapfile; sudo swapon /swapfile

1024000+0 records in
1024000+0 records out
1048576000 bytes (1.0 GB) copied, 48.22 s, 21.7 MB/s
Setting up swapspace version 1, size = 1048571 kB
no label, UUID=1c269910-c4f4-441d-a65c-3cd0ff2a4f31

free -tom
             total       used       free     shared    buffers     cached
Mem:          1010        997         13          0          1        400
Swap:         3047         64       2983
Total:        4057       1061       2996

By: dcabanis
2009-05-27 21:10:50

These Might Interest You

  • In addition to a swap partition, Linux can also use a swap file. Some programs, like g++, can use huge amounts of virtual memory, requiring the temporary creation of extra space.

    dd if=/dev/zero of=/swapfile bs=1M count=64; chmod 600 /swapfile; mkswap /swapfile; swapon /swapfile
    starchox · 2009-02-16 18:36:38 0
  • Col 1 is swapped sum in kb Col 2 is pid of process Col 3 is command that was issued Show Sample Output

    for i in $(ps -ef | awk '{print $2}') ; { swp=$( awk '/Swap/{sum+=$2} END {print sum}' /proc/$i/smaps ); if [[ -n $swp && 0 != $swp ]] ; then echo -n "\n $swp $i "; cat /proc/$i/cmdline ; fi; } | sort -nr
    cbrinker · 2010-01-22 00:09:46 0
  • When you run a memory intensive application (VirtualBox, large java application, etc) swap area is used as soon as memory becomes insufficient. After you close the program, the data in swap is not put back on memory and that decreases the responsiveness. Swapoff disables the swap area and forces system to put swap data be placed in memory. Since running without a swap area might be detrimental, swapon should be used to activate swap again. Both swapoff and swapon require root privileges.

    swapoff -a ; swapon -a
    alperyilmaz · 2009-03-25 03:30:41 0
  • Report memory and swap space utilization statistics e.g. memory free/used, swap free/used

    sar -r
    sharfah · 2009-05-19 11:47:38 2

  • -1
    echo | socat -u - file:/tmp/swapfile,create,largefile,seek=10000000000000
    madrasi · 2011-02-08 00:30:38 1
  • This awk command prints a histogram of the number of times 'emergency' is the first word in a line, per day, in an irssi (IRC client) log file. Show Sample Output

    awk '/^--- Day changed (.*)/ {st=""; for (i=0;i<ar[date];i++) {st=st"*"} print date" "st; date=$7"-"$5"-"$6} /> emergency/ {ar[date]++} END {st=""; for (i=0;i<ar[date];i++) {st=st"*"}; print date" "st}' #engineyard.log
    menicosia · 2010-02-24 22:54:34 1

What Others Think

sudo bximage -hd -mode=flat -size=1024 -q /swapfile; sudo mkswap /swapfile; sudo swapon /swapfile As it is much less resource (i.e. cpu and hd) consuming time dd if=/dev/zero of=/swapfile bs=1024 count=1024000 (...) dd if=/dev/zero of=/swapfile bs=1024 count=1024000 0.33s user 7.34s system 34% cpu 22.552 total time bximage -hd -mode=flat -size=1024 -q .swapfile (...) bximage -hd -mode=flat -size=1024 -q /swapfile 0.00s user 0.00s system 58% cpu 0.005 total time /sbin/mkswap /swapfile mkswap: d.img: warning: don't erase bootbits sectors on whole disk. Use -f to force. Setting up swapspace version 1, size = 1048316 KiB no label, UUID=xxxxxxxx /sbin/mkswap /swapfile 0.00s user 0.00s system 0% cpu 0.647 total bximage is part of boche emulator - but is is suitable as we are not interested in any particular content (zero) so we don't mind garbage inside.
MaciejPiechotka · 468 weeks and 6 days ago

What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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