Ubuntu – How to selectively purge old kernels all at once

aptbootgrub2kernel

The highly rated Q&A How do I remove old kernel versions to clean up the boot menu? doesn't provide an easy way to selectively purge older kernels unless extra applications are installed ie Ubuntu-Tweak.

The Bash one-liner to delete only old kernels Q&A gives a "purge everything old" solution but I want to keep the last kernel in each generation. ie remove 4.7.1, 4.7.2… but keep 4.7.5.

Is there a way to scroll through a list of all installed kernels and select specific ones to purge? It should not allow purging of currently running kernel.

Best Answer

  • The advantage of this answer is native Ubuntu Bash is used without installing third-party applications. Users of custom kernels who didn't use apt or dpkg can change this bash script to suit their needs.

    Zenity based solution

    Zenity provides a GUI interface to the terminal. Here it's used to process a list of kernels and select individual ones:

    rm-kernels 1.png

    The dialog title reports the number of kernels, their total size and the current kernel version booted. The current kernel is excluded from the title's totals and does not appear the kernel list.

    The Modified Date is normally the date the kernel was released. On my system that date is "touched" every time the kernel is booted using a cron reboot script (How do you find out when a specific kernel version was last booted?).

    For each kernel its size within the /boot directory is reported. Then the kernel's total size is summed for the three directories; /boot, /usr/src/kernel_version and /lib/modules/kernel_version.

    If no parameter is passed to rm-kernels the total size is estimated and the title shows "Est. Total". This saves time running the du command which can take 30 seconds to 90 minutes depending on how many kernels you have and whether you have an SSD or an HDD. If you pass any parameter at all then du is used to obtain kernel sizes and the title shows "Real Total" as the sample screen above illustrates.

    apt-get purge gives you chance to abort

    You get to view everything that will be purged by apt purge and are given the option to proceed or abort:

    The following packages will be REMOVED:
      linux-headers-4.4.0-78* linux-headers-4.4.0-78-generic*
      linux-headers-4.4.8-040408* linux-headers-4.4.8-040408-generic*
      linux-headers-4.6.3-040603* linux-headers-4.6.3-040603-generic*
      linux-headers-4.8.12-040812* linux-headers-4.8.12-040812-generic*
      linux-headers-4.9.0-040900* linux-headers-4.9.0-040900-generic*
      linux-headers-4.9.9-040909* linux-headers-4.9.9-040909-generic*
      linux-image-4.4.0-78-generic* linux-image-4.4.8-040408-generic*
      linux-image-4.6.3-040603-generic* linux-image-4.8.12-040812-generic*
      linux-image-4.9.0-040900-generic* linux-image-4.9.9-040909-generic*
      linux-image-extra-4.4.0-78-generic*
    0 upgraded, 0 newly installed, 19 to remove and 1 not upgraded.
    After this operation, 1,794 MB disk space will be freed.
    Do you want to continue? [Y/n] 
    

    apt purge reports 1,784 MB will be freed but the real total 2,379 MB. I don't know why it is different.

    Rather than purging kernels one at a time and update-grub being repetitively called in time-consuming loop, the selections are purged all at once.

    The Code

    Copy this code to a file named rm-kernels in /usr/local/bin:

    #!/bin/bash
    
    # NAME: rm-kernels
    # PATH: /usr/local/bin
    # DESC: Provide zenity item list of kernels to remove
    
    # DATE: Mar 10, 2017. Modified Aug 5, 2017.
    
    # NOTE: Will not delete current kernel.
    
    #       With 10 kernels on an SSD, empty cache from sudo prompt (#) using:
    #       # free && sync && echo 3 > /proc/sys/vm/drop_caches && free
    #       First time for `du` 34 seconds.
    #       Second time for `du` 1 second.
    #       With a magnetic hard disk, and empty memory cache:
    #       the first `du` command averages about 20 seconds per kernel.
    #       the second `du` command averages about 2.5 seconds per kernel.
    
    # PARM: If any parm 1 passed use REAL kernel size, else use estimated size.
    #       By default `du` is not used and estimated size is displayed.
    
    # Must be running as sudo
    if [[ $(id -u) != 0 ]]; then
        zenity --error --text "root access required. Use: sudo rm-kernels"
        exit 99
    fi
    
    OLDIFS="$IFS"
    IFS="|"
    choices=()
    
    current_version=$(uname -r)
    
    for f in /boot/vmlinuz*
    do
        if [[ $f == *"$current_version"* ]]; then continue; fi # skip current version
        [[ $f =~ vmlinuz-(.*) ]]
        v=${BASH_REMATCH[1]}        # example: 4.9.21-040921-generic
        v_main="${v%-*}"            # example: 4.9.21-040921
    
        n=$(( n + 1 ))              # increment number of kernels
    
        # Kernel size in /boot/*4.9.21-040921-generic*
        s=$(du -ch /boot/*-$v* | awk '/total/{print $1}')
    
        if [[ $# -ne 0 ]] ; then    # Was a parameter passed?
            if [[ -d "/usr/src/linux-headers-"$v_main ]] ; then
                 # Kernel headers size in /usr/src/*4.9.21-040921*
                 s2=$(du -ch --max-depth=1 /usr/src/*-$v_main* | awk '/total/{print $1}')
            else
                 s2="0M"            # Linux Headers are not installed
            fi
            # Kernel image size in /lib/modules/4.9.21-040921-generic*
            s3=$(du -ch --max-depth=1 /lib/modules/$v* | awk '/total/{print $1}')
        else
            # Estimate sizof of optional headers at 125MB and size of image at 220MB
            if [[ -d "/usr/src/linux-headers-"$v_main ]] ; then
                 s2="125M"
            else
                 s2="0M"            # Linux Headers are not installed
            fi
            s3="220M"
        fi
    
        # Strip out "M" provided by human readable option of du and add 3 sizes together
        c=$(( ${s//[^0-9]*} + ${s2//[^0-9]*} + ${s3//[^0-9]*} ))
        s=$(( ${s//[^0-9]*} )) # Strip out M to make " MB" below which looks nicer
        t=$(( t + c ))
        s=$s" MB"
        c=$c" MB"
        d=$(date --date $(stat -c %y $f) '+%b %d %Y') # Last modified date for display
        choices=("${choices[@]}" false "$v" "$d" "$s" "$c")
    done
    
    # Write Kernel version and array index to unsorted file
    > ~/.rm-kernels-plain # Empty any existing file.
    for (( i=1; i<${#choices[@]}; i=i+5 )) ; do
        echo "${choices[i]}|$i" >> ~/.rm-kernels-plain
    done
    
    # Sort kernels by version number
    sort -V -k1 -t'|' ~/.rm-kernels-plain -o ~/.rm-kernels-sorted
    
    # Strip out keys leaving Sorted Index Numbers
    cut -f2 -d '|' ~/.rm-kernels-sorted > ~/.rm-kernels-ndx
    
    # Create sorted array
    SortedArr=()
    while read -r ndx; do 
        end=$(( ndx + 4 ))
        for (( i=$(( ndx - 1 )); i<end; i++ )); do
            SortedArr+=("${choices[i]}")
        done
    done < ~/.rm-kernels-ndx
    
    rm ~/.rm-kernels-plain ~/.rm-kernels-sorted ~/.rm-kernels-ndx
    
    if [[ $# -ne 0 ]] ; then    # Was a parameter passed?
        VariableHeading="Real Total"
    else
        VariableHeading="Est. Total"
    fi
    
    # adjust width & height below for your screen 640x480 default for 1920x1080 HD screen
    # also adjust font="14" below if blue text is too small or too large
    
    choices=(`zenity \
            --title "rm-kernels - $n Kernels, Total: $t MB excluding: $current_version" \
            --list \
            --separator="$IFS" \
            --checklist --multiple \
            --text '<span foreground="blue" font="14">Check box next to kernel(s) to remove</span>' \
            --width=800 \
            --height=480 \
            --column "Select" \
            --column "Kernel Version Number" \
            --column "Modified Date" \
            --column "/boot Size" \
            --column "$VariableHeading" \
            "${SortedArr[@]}"`)
    IFS="$OLDIFS"
    
    i=0
    list=""
    for choice in "${choices[@]}" ; do
        if [ "$i" -gt 0 ]; then list="$list- "; fi # append "-" from last loop
        ((i++))
    
        short_choice=$(echo $choice | cut -f1-2 -d"-")
        header_count=$(find /usr/src/linux-headers-$short_choice* -maxdepth 0 -type d | wc -l)
    
        # If -lowlatency and -generic are purged at same time the _all header directory
        # remains on disk for specific version with no -generic or -lowlatency below.
        if [[ $header_count -lt 3 ]]; then
            # Remove all w.x.y-zzz headers
            list="$list""linux-image-$choice- linux-headers-$short_choice"
        else
            # Remove w.x.y-zzz-flavour header only, ie -generic or -lowlatency
            list="$list""linux-image-$choice- linux-headers-$choice" 
        fi
    
    done
    
    if [ "$i" -gt 0 ] ; then
         apt-get purge $list
    fi
    

    NOTE: You need to use sudo powers to save the file with your favorite editor.

    To make file executable use:

    sudo chmod +x /usr/local/bin/rm-kernels
    

    Server Version

    rm-kernels-server is the server version to selectively delete kernels all at once. Instead of a GUI (graphical) dialog box a text-based dialog box is used to select kernels to purge.

    • Before running the script you need to install the dialog function using:

      sudo apt install dialog

    Dialog is in the default Ubuntu Desktop installation but not in Ubuntu Server.

    Sample screen

    rm-kernels-server 1

    rm-kernels-server bash code

    #!/bin/bash
    
    # NAME: rm-kernels-server
    # PATH: /usr/local/bin
    # DESC: Provide dialog checklist of kernels to remove
    #       Non-GUI, text based interface for server distro's.
    
    # DATE: Mar 10, 2017. Modified Aug 5, 2017.
    
    # NOTE: Will not delete current kernel.
    
    #       With 10 kernels on an SSD, empty cache from sudo prompt (#) using:
    #       # free && sync && echo 3 > /proc/sys/vm/drop_caches && free
    #       First time for `du` 34 seconds.
    #       Second time for `du` 1 second.
    #       With a magnetic hard disk, and empty memory cache:
    #       the first `du` command averages about 20 seconds per kernel.
    #       the second `du` command averages about 2.5 seconds per kernel.
    
    # PARM: If any parm 1 passed use REAL kernel size, else use estimated size.
    #       By default `du` is not used and estimated size is displayed.
    
    # Must be running as sudo
    if [[ $(id -u) != 0 ]]; then
        echo "root access required. Use: sudo rm-kernels-server"
        exit 99
    fi
    
    # Must have the dialog package. On Servers, not installed by default
    command -v dialog >/dev/null 2>&1 || { echo >&2 "dialog package required but it is not installed.  Aborting."; exit 99; }
    
    OLDIFS="$IFS"
    IFS="|"
    item_list=() # Deviate from rm-kernels here.
    
    current_version=$(uname -r)
    i=0
    for f in /boot/vmlinuz*
    do
        if [[ $f == *"$current_version"* ]]; then continue; fi # skip current version
        [[ $f =~ vmlinuz-(.*) ]]
        ((i++)) # Item List
        v=${BASH_REMATCH[1]}        # example: 4.9.21-040921-generic
        v_main="${v%-*}"            # example: 4.9.21-040921
    
        n=$(( n + 1 ))              # increment number of kernels
    
        # Kernel size in /boot/*4.9.21-040921-generic*
        s=$(du -ch /boot/*-$v* | awk '/total/{print $1}')
    
        if [[ $# -ne 0 ]] ; then    # Was a parameter passed?
            if [[ -d "/usr/src/linux-headers-"$v_main ]] ; then
                 # Kernel headers size in /usr/src/*4.9.21-040921*
                 s2=$(du -ch --max-depth=1 /usr/src/*-$v_main* | awk '/total/{print $1}')
            else
                 s2="0M"            # Linux Headers are not installed
            fi
            # Kernel image size in /lib/modules/4.9.21-040921-generic*
            s3=$(du -ch --max-depth=1 /lib/modules/$v* | awk '/total/{print $1}')
        else
            # Estimate sizof of optional headers at 125MB and size of image at 220MB
            if [[ -d "/usr/src/linux-headers-"$v_main ]] ; then
                 s2="125M"
            else
                 s2="0M"            # Linux Headers are not installed
            fi
            s3="220M"
        fi
    
        # Strip out "M" provided by human readable option of du and add 3 sizes together
        c=$(( ${s//[^0-9]*} + ${s2//[^0-9]*} + ${s3//[^0-9]*} ))
        s=$(( ${s//[^0-9]*} )) # Strip out M to make " MB" below which looks nicer
        t=$(( t + c ))
        s=$s" MB"
        c=$c" MB"
        d=$(date --date $(stat -c %y $f) '+%b %d %Y') # Last modified date for display
        item_list=("${item_list[@]}" "$i" "$v ! $d ! $s ! $c" off)
    done
    
    # Write Kernel version and array index to unsorted file
    > ~/.rm-kernels-plain # Empty any existing file.
    for (( i=1; i<${#item_list[@]}; i=i+3 )) ; do
        echo "${item_list[i]}|$i" >> ~/.rm-kernels-plain
    done
    
    # Sort kernels by version number
    sort -V -k1 -t'|' ~/.rm-kernels-plain -o ~/.rm-kernels-sorted
    
    # Strip out keys leaving Sorted Index Numbers
    cut -f2 -d '|' ~/.rm-kernels-sorted > ~/.rm-kernels-ndx
    
    # Create sorted array
    SortedArr=()
    i=1
    while read -r ndx; do 
        SortedArr+=($i "${item_list[$ndx]}" "off")
        (( i++ ))
    done < ~/.rm-kernels-ndx
    
    rm ~/.rm-kernels-plain ~/.rm-kernels-sorted ~/.rm-kernels-ndx
    
    cmd=(dialog --backtitle "rm-kernels-server - $n Kernels, Total: $t MB excluding: $current_version" \
        --title "Use space bar to toggle kernel(s) to remove" \
        --column-separator "!" \
        --separate-output \
        --ascii-lines \
        --checklist "         Kernel Version  ------  Modified Date /boot Size  Total" 20 70 15)
    
    selections=$("${cmd[@]}" "${SortedArr[@]}" 2>&1 >/dev/tty)
    
    IFS=$OLDIFS
    
    if [ $? -ne 0 ] ; then
        echo cancel selected
        exit 1
    fi
    
    i=0
    choices=()
    
    for select in $selections ; do
        ((i++))
        j=$(( 1 + ($select - 1) * 3 ))
        choices[i]=$(echo ${SortedArr[j]} | cut -f1 -d"!")
    done
    
    i=0
    list=""
    for choice in "${choices[@]}" ; do
        if [ "$i" -gt 0 ]; then list="$list- "; fi # append "-" from last loop
        ((i++))
    
        short_choice=$(echo $choice | cut -f1-2 -d"-")
        header_count=$(find /usr/src/linux-headers-$short_choice* -maxdepth 0 -type d | wc -l)
    
        # If -lowlatency and -generic are purged at same time the _all header directory
        # remains on disk for specific version with no -generic or -lowlatency below.
        if [[ $header_count -lt 3 ]]; then
            # Remove all w.x.y-zzz headers
            list="$list""linux-image-$choice- linux-headers-$short_choice"
        else
            # Remove w.x.y-zzz-flavour header only, ie -generic or -lowlatency
            list="$list""linux-image-$choice- linux-headers-$choice" 
        fi
    
    done
    
    if [ "$i" -gt 0 ] ; then
        apt-get purge $list
    fi
    

    NOTE: In the call to dialog the directive --ascii-lines is passed to replace line-draw extended character set (which ssh doesn't like) with "+-----+" for drawing boxes. If you do not like this appearance you can use the --no-lines directive for no box at all. If you aren't using ssh you can delete the --ascii-lines and your display will be formated with line-draw characters:

    rm-kernels-server line draw


    July 28, 2017 Updates

    The calculated size of each kernel was taken from /boot/*kernel_version* which were 5 files totaling ~50 MB. The formula has changed to include the files in /usr/src/*kernel_version* and /lib/modules/*kernel_version*. The calculated size for each kernel is now ~400 MB.

    The default is to estimate the size of files for linux-headers at 125 MB and linux-image at 220 MB because du can be painfully slow unless files are in cached in memory. To get the real size using du pass any parameter to the script.

    The total of all kernel sizes (excluding the current running version which cannot be removed) is now show in the title bar.

    The dialog box used to display each Kernel's Last Access Date. This date can get mass overwritten for all kernels during backup or similar operations. The dialog box now shows the Modified Date instead.


    August 5, 2017 Updates

    The kernel list is now sorted by Kernel Version rather than alpha-numerically.

    An additional column has been added for /boot size. In the graphical Zenity version the last column changes between "Real Total" and "Est. Total" (Estimated) depending on parameter 1 being passed or not.