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You can use either of these two one-liners. Both yield the exact same output on my machine and are more precise than all solutions proposed up until now (July 2014) in this question. They are a combination of the two answers (1) and (2). Note that I originally posted this answer here.

Using apt-mark:

comm -23 <(apt-mark showmanual | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Using aptitude:

comm -23 <(aptitude search '~i !~M' -F '%p' | sed "s/ *$//" | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Very few packages still fall through the cracks, although I suspect these are actually installed by the user, either right after the installation through the language localization setup or e.g. through the Totem codec installer. Also, the linux-header versions also seem to accumulate, even though I've only installed the non version-specific metapackage. Examples:

libreoffice-help-en-gb
openoffice.org-hyphenation
gstreamer0.10-fluendo-mp3
linux-headers-3.13.0-29    

How does it work

1. Get the list of manually installed packages. For aptitude, the additional sed strips out remaining whitespace at the end of the line.
2. Get the list of packages installed right after a fresh install.
3. Compare the files, only output the lines in file 1 that are not present in file 2.

Other possibilities don't work as well:

• Using the ubuntu-14.04-desktop-amd64.manifest file (here for Ubuntu 14.04) instead of /var/log/installer/initial-status.gz. More packages are shown as manually installed even though they are not.
• Using apt-mark showauto instead of /var/log/installer/initial-status.gz. apt-mark for example doesn't include the xserver-xorg package, while the other file does.

Both list more packages than the above solution.

You can use either of these two one-liners. Both yield the exact same output on my machine and are more precise than all solutions proposed up until now (July 2014) in this question. They are a combination of the two answers (1) and (2). Note that I originally posted this answer here.

Using apt-mark:

comm -23 <(apt-mark showmanual | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Using aptitude:

comm -23 <(aptitude search '~i !~M' -F '%p' | sed "s/ *$//" | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Very few packages still fall through the cracks, although I suspect these are actually installed by the user, either right after the installation through the language localization setup or e.g. through the Totem codec installer. Also, the linux-header versions also seem to accumulate, even though I've only installed the non version-specific metapackage. Examples:

libreoffice-help-en-gb
openoffice.org-hyphenation
gstreamer0.10-fluendo-mp3
linux-headers-3.13.0-29    

How does it work

1. Get the list of manually installed packages. For aptitude, the additional sed strips out remaining whitespace at the end of the line.
2. Get the list of packages installed right after a fresh install.
3. Compare the files, only output the lines in file 1 that are not present in file 2.

Other possibilities don't work as well:

• Using the ubuntu-14.04-desktop-amd64.manifest file (here for Ubuntu 14.04) instead of /var/log/installer/initial-status.gz. More packages are shown as manually installed even though they are not.
• Using apt-mark showauto instead of /var/log/installer/initial-status.gz. apt-mark for example doesn't include the xserver-xorg package, while the other file does.

Both list more packages than the above solution.

You can use either of these two one-liners. Both yield the exact same output on my machine and are more precise than all solutions proposed up until now (July 2014) in this question. They are a combination of the two answers (1) and (2). Note that I originally posted this answer here.

Using apt-mark:

comm -23 <(apt-mark showmanual | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Using aptitude:

comm -23 <(aptitude search '~i !~M' -F '%p' | sed "s/ *$//" | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Very few packages still fall through the cracks, although I suspect these are actually installed by the user, either right after the installation through the language localization setup or e.g. through the Totem codec installer. Also, the linux-header versions also seem to accumulate, even though I've only installed the non version-specific metapackage. Examples:

libreoffice-help-en-gb
openoffice.org-hyphenation
gstreamer0.10-fluendo-mp3
linux-headers-3.13.0-29    

How does it work

1. Get the list of manually installed packages. For aptitude, the additional sed strips out remaining whitespace at the end of the line.
2. Get the list of packages installed right after a fresh install.
3. Compare the files, only output the lines in file 1 that are not present in file 2.

Other possibilities don't work as well:

• Using the ubuntu-14.04-desktop-amd64.manifest file (here for Ubuntu 14.04) instead of /var/log/installer/initial-status.gz. More packages are shown as manually installed even though they are not.
• Using apt-mark showauto instead of /var/log/installer/initial-status.gz. apt-mark for example doesn't include the xserver-xorg package, while the other file does.

Both list more packages than the above solution.

You can use either of these two one-liners. Both yield the exact same output on my machine and are more precise than all solutions proposed up until now (July 2014) in this question. They are a combination of the two answers (1) and (2). Note that I originally posted this answer here.

Using apt-mark:

comm -23 <(apt-mark showmanual | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Using aptitude:

comm -23 <(aptitude search '~i !~M' -F '%p' | sed "s/ *$//" | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Very few packages still fall through the cracks, although I suspect these are actually installed by the user, either right after the installation through the language localization setup or e.g. through the Totem codec installer. Also, the linux-header versions also seem to accumulate, even though I've only installed the non version-specific metapackage. Examples:

libreoffice-help-en-gb
openoffice.org-hyphenation
gstreamer0.10-fluendo-mp3
linux-headers-3.13.0-29    

How does it work

1. Get the list of manually installed packages. For aptitude, the additional sed strips out remaining whitespace at the end of the line.
2. Get the list of packages installed right after a fresh install.
3. Compare the files, only output the lines in file 1 that are not present in file 2.

Other possibilities don't work as well:

• Using the ubuntu-14.04-desktop-amd64.manifest file (here for Ubuntu 14.04) instead of /var/log/installer/initial-status.gz. More packages are shown as manually installed even though they are not.
• Using apt-mark showauto instead of /var/log/installer/initial-status.gz. apt-mark for example doesn't include the xserver-xorg package, while the other file does.

Both list more packages than the above solution.

You can use either of these two one-liners. Both yield the exact same output on my machine and are more precise than all solutions proposed up until now in this question. They are a combination of the two answers (1) and (2). Note that I originally posted this answer here.

Using apt-mark:

comm -23 <(apt-mark showmanual | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Using aptitude:

comm -23 <(aptitude search '~i !~M' -F '%p' | sed "s/ *$//" | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Very few packages still fall through the cracks, although I suspect these are actually installed by the user, either right after the installation through the language localization setup or e.g. through the Totem codec installer. Also, the linux-header versions also seem to accumulate, even though I've only installed the non version-specific metapackage. Examples:

libreoffice-help-en-gb
openoffice.org-hyphenation
gstreamer0.10-fluendo-mp3
linux-headers-3.13.0-29    

How does it work

1. Get the list of manually installed packages. For aptitude, the additional sed strips out remaining whitespace at the end of the line.
2. Get the list of packages installed right after a fresh install.
3. Compare the files, only output the lines in file 1 that are not present in file 2.

Other possibilities don't work as well:

• Using the ubuntu-14.04-desktop-amd64.manifest file (here for Ubuntu 14.04) instead of /var/log/installer/initial-status.gz. More packages are shown as manually installed even though they are not.
• Using apt-mark showauto instead of /var/log/installer/initial-status.gz. apt-mark for example doesn't include the xserver-xorg package, while the other file does.

Both list more packages than the above solution.

You can use either of these two one-liners. Both yield the exact same output on my machine and are more precise than all solutions proposed up until now (July 2014) in this question. They are a combination of the two answers (1) and (2). Note that I originally posted this answer here.

Using apt-mark:

comm -23 <(apt-mark showmanual | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Using aptitude:

comm -23 <(aptitude search '~i !~M' -F '%p' | sed "s/ *$//" | sort -u) <(gzip -dc /var/log/installer/initial-status.gz | sed -n 's/^Package: //p' | sort -u)

Very few packages still fall through the cracks, although I suspect these are actually installed by the user, either right after the installation through the language localization setup or e.g. through the Totem codec installer. Also, the linux-header versions also seem to accumulate, even though I've only installed the non version-specific metapackage. Examples:

libreoffice-help-en-gb
openoffice.org-hyphenation
gstreamer0.10-fluendo-mp3
linux-headers-3.13.0-29    

How does it work

1. Get the list of manually installed packages. For aptitude, the additional sed strips out remaining whitespace at the end of the line.
2. Get the list of packages installed right after a fresh install.
3. Compare the files, only output the lines in file 1 that are not present in file 2.

Other possibilities don't work as well:

• Using the ubuntu-14.04-desktop-amd64.manifest file (here for Ubuntu 14.04) instead of /var/log/installer/initial-status.gz. More packages are shown as manually installed even though they are not.
• Using apt-mark showauto instead of /var/log/installer/initial-status.gz. apt-mark for example doesn't include the xserver-xorg package, while the other file does.

Both list more packages than the above solution.