How does `update-alternatives --config somecommand` find the symlinks for `somecommand`?
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From https://stackoverflow.com/a/48374564/156458
update-alternatives --config javaworks by installing symlinks to commands as/usr/bin/java,/usr/bin/javacand so on.
How does update-alternatives --config somecommand find the symlinks for somecommand?
For example, does it rely on $PATH, and therefore work in the same way as how bash find the files for somecommand when running somecommand directly in bash?
If the file for somecommand is not a symlink, will update-alternative --config somecommand work?
Thanks.
software-installation path alternatives
asked Jan 22 at 13:09
Tim
22.7k65224403
add a comment |Â
up vote
1
down vote
favorite
From https://stackoverflow.com/a/48374564/156458
update-alternatives --config javaworks by installing symlinks to commands as/usr/bin/java,/usr/bin/javacand so on.
How does update-alternatives --config somecommand find the symlinks for somecommand?
For example, does it rely on $PATH, and therefore work in the same way as how bash find the files for somecommand when running somecommand directly in bash?
If the file for somecommand is not a symlink, will update-alternative --config somecommand work?
Thanks.
software-installation path alternatives
asked Jan 22 at 13:09
Tim
22.7k65224403
1
I usually (ab)useltraceandstracefor those quick doubts.
– Rui F Ribeiro
Jan 22 at 13:28
Or, list the contents of the package that provides the command/binary, and traverse the directories and read its manpage(s).
– ILMostro_7
Jan 22 at 13:42
add a comment |Â
up vote
1
down vote
favorite
up vote
1
down vote
favorite
From https://stackoverflow.com/a/48374564/156458
update-alternatives --config javaworks by installing symlinks to commands as/usr/bin/java,/usr/bin/javacand so on.
How does update-alternatives --config somecommand find the symlinks for somecommand?
For example, does it rely on $PATH, and therefore work in the same way as how bash find the files for somecommand when running somecommand directly in bash?
If the file for somecommand is not a symlink, will update-alternative --config somecommand work?
Thanks.
software-installation path alternatives
asked Jan 22 at 13:09
Tim
22.7k65224403
From https://stackoverflow.com/a/48374564/156458
update-alternatives --config javaworks by installing symlinks to commands as/usr/bin/java,/usr/bin/javacand so on.
How does update-alternatives --config somecommand find the symlinks for somecommand?
For example, does it rely on $PATH, and therefore work in the same way as how bash find the files for somecommand when running somecommand directly in bash?
If the file for somecommand is not a symlink, will update-alternative --config somecommand work?
Thanks.
software-installation path alternatives
asked Jan 22 at 13:09
Tim
22.7k65224403
asked Jan 22 at 13:09
Tim
22.7k65224403
asked Jan 22 at 13:09
Tim
22.7k65224403
asked Jan 22 at 13:09
Tim
22.7k65224403
22.7k65224403
1
I usually (ab)useltraceandstracefor those quick doubts.
– Rui F Ribeiro
Jan 22 at 13:28
Or, list the contents of the package that provides the command/binary, and traverse the directories and read its manpage(s).
– ILMostro_7
Jan 22 at 13:42
add a comment |Â
1
I usually (ab)useltraceandstracefor those quick doubts.
– Rui F Ribeiro
Jan 22 at 13:28
Or, list the contents of the package that provides the command/binary, and traverse the directories and read its manpage(s).
– ILMostro_7
Jan 22 at 13:42
1
1
I usually (ab)use
ltrace and strace for those quick doubts.– Rui F Ribeiro
Jan 22 at 13:28
I usually (ab)use
ltrace and strace for those quick doubts.– Rui F Ribeiro
Jan 22 at 13:28
Or, list the contents of the package that provides the command/binary, and traverse the directories and read its manpage(s).
– ILMostro_7
Jan 22 at 13:42
Or, list the contents of the package that provides the command/binary, and traverse the directories and read its manpage(s).
– ILMostro_7
Jan 22 at 13:42
add a comment |Â
1 Answer
1
active
oldest
votes
up vote
4
down vote
accepted
The way update-alternatives works is described in its manpage. The list of available alternatives for a given command (or file, in general — alternatives aren’t limited to commands) is stored in a file in /var/lib/dpkg/alternatives on Debian and derivatives; thus the alternatives for java are stored in /var/lib/dpkg/alternatives/java. On Fedora, RHEL, and derivatives, the files are stored in /var/lib/alternatives.
When a package wishes to provide an alternative, it installs it using update-alternatives --install (and appropriate parameters); when it wishes to remove an alternative, it does so using update-alternatives --remove. You can use these to provide your own alternatives if necessary.
Note that in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually.
If for some reason an alternative-managed file is not a symlink, update-alternatives will consider that the alternative is broken and will refuse to touch it.
answered Jan 22 at 13:15
Stephen Kitt
142k22308371
Interesting note about java alternatives there. I'm not at all familiar with how or why that would be the case, however usingupdate-alternativeshas always worked for me when dealing with java. Additionally, while the original work was created by debian developers, RedHat-based distros have adapted it as well. Although, there is no specificupdate-java-alternativescommand on RHEL, e.g. It might be worth noting as well, on RedHat-based systems, the path is/var/lib/alternativesfor the alternative scripts.
– ILMostro_7
Jan 22 at 13:48
1
@ILMostro_7 right,update-alternativesstill works,update-java-alternativesmakes it easier to update all the JRE/JDK-provided tools when changing JVMs (look at the/var/lib/jvm/.*.jinfofiles for details). Thanks for the comment, I’ve updated my answer.
– Stephen Kitt
Jan 22 at 13:51
Thanks. Why "in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually" ? I am reading askubuntu.com/questions/159575/…, but still can't figure it out.
– Tim
Jan 22 at 15:28
@Tim, for Java packages, there are lots of different alternatives, none of which are connected (partly because you might only have a sub-selection of the commands installed); so if you want to switch from Java 8 to Java 9 for example, you’d have to update a couple of dozen alternatives manually...update-java-alternativesdoes that for you.
– Stephen Kitt
Jan 22 at 15:30
What are " a couple of dozen alternatives" that I have to update manually? Is$JAVA_HOMEincluded?
– Tim
Jan 22 at 15:39
 |Â
show 7 more comments
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
accepted
The way update-alternatives works is described in its manpage. The list of available alternatives for a given command (or file, in general — alternatives aren’t limited to commands) is stored in a file in /var/lib/dpkg/alternatives on Debian and derivatives; thus the alternatives for java are stored in /var/lib/dpkg/alternatives/java. On Fedora, RHEL, and derivatives, the files are stored in /var/lib/alternatives.
When a package wishes to provide an alternative, it installs it using update-alternatives --install (and appropriate parameters); when it wishes to remove an alternative, it does so using update-alternatives --remove. You can use these to provide your own alternatives if necessary.
Note that in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually.
If for some reason an alternative-managed file is not a symlink, update-alternatives will consider that the alternative is broken and will refuse to touch it.
answered Jan 22 at 13:15
Stephen Kitt
142k22308371
Interesting note about java alternatives there. I'm not at all familiar with how or why that would be the case, however usingupdate-alternativeshas always worked for me when dealing with java. Additionally, while the original work was created by debian developers, RedHat-based distros have adapted it as well. Although, there is no specificupdate-java-alternativescommand on RHEL, e.g. It might be worth noting as well, on RedHat-based systems, the path is/var/lib/alternativesfor the alternative scripts.
– ILMostro_7
Jan 22 at 13:48
1
@ILMostro_7 right,update-alternativesstill works,update-java-alternativesmakes it easier to update all the JRE/JDK-provided tools when changing JVMs (look at the/var/lib/jvm/.*.jinfofiles for details). Thanks for the comment, I’ve updated my answer.
– Stephen Kitt
Jan 22 at 13:51
Thanks. Why "in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually" ? I am reading askubuntu.com/questions/159575/…, but still can't figure it out.
– Tim
Jan 22 at 15:28
@Tim, for Java packages, there are lots of different alternatives, none of which are connected (partly because you might only have a sub-selection of the commands installed); so if you want to switch from Java 8 to Java 9 for example, you’d have to update a couple of dozen alternatives manually...update-java-alternativesdoes that for you.
– Stephen Kitt
Jan 22 at 15:30
What are " a couple of dozen alternatives" that I have to update manually? Is$JAVA_HOMEincluded?
– Tim
Jan 22 at 15:39
 |Â
show 7 more comments
up vote
4
down vote
accepted
The way update-alternatives works is described in its manpage. The list of available alternatives for a given command (or file, in general — alternatives aren’t limited to commands) is stored in a file in /var/lib/dpkg/alternatives on Debian and derivatives; thus the alternatives for java are stored in /var/lib/dpkg/alternatives/java. On Fedora, RHEL, and derivatives, the files are stored in /var/lib/alternatives.
When a package wishes to provide an alternative, it installs it using update-alternatives --install (and appropriate parameters); when it wishes to remove an alternative, it does so using update-alternatives --remove. You can use these to provide your own alternatives if necessary.
Note that in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually.
If for some reason an alternative-managed file is not a symlink, update-alternatives will consider that the alternative is broken and will refuse to touch it.
answered Jan 22 at 13:15
Stephen Kitt
142k22308371
Interesting note about java alternatives there. I'm not at all familiar with how or why that would be the case, however usingupdate-alternativeshas always worked for me when dealing with java. Additionally, while the original work was created by debian developers, RedHat-based distros have adapted it as well. Although, there is no specificupdate-java-alternativescommand on RHEL, e.g. It might be worth noting as well, on RedHat-based systems, the path is/var/lib/alternativesfor the alternative scripts.
– ILMostro_7
Jan 22 at 13:48
1
@ILMostro_7 right,update-alternativesstill works,update-java-alternativesmakes it easier to update all the JRE/JDK-provided tools when changing JVMs (look at the/var/lib/jvm/.*.jinfofiles for details). Thanks for the comment, I’ve updated my answer.
– Stephen Kitt
Jan 22 at 13:51
Thanks. Why "in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually" ? I am reading askubuntu.com/questions/159575/…, but still can't figure it out.
– Tim
Jan 22 at 15:28
@Tim, for Java packages, there are lots of different alternatives, none of which are connected (partly because you might only have a sub-selection of the commands installed); so if you want to switch from Java 8 to Java 9 for example, you’d have to update a couple of dozen alternatives manually...update-java-alternativesdoes that for you.
– Stephen Kitt
Jan 22 at 15:30
What are " a couple of dozen alternatives" that I have to update manually? Is$JAVA_HOMEincluded?
– Tim
Jan 22 at 15:39
 |Â
show 7 more comments
up vote
4
down vote
accepted
up vote
4
down vote
accepted
The way update-alternatives works is described in its manpage. The list of available alternatives for a given command (or file, in general — alternatives aren’t limited to commands) is stored in a file in /var/lib/dpkg/alternatives on Debian and derivatives; thus the alternatives for java are stored in /var/lib/dpkg/alternatives/java. On Fedora, RHEL, and derivatives, the files are stored in /var/lib/alternatives.
When a package wishes to provide an alternative, it installs it using update-alternatives --install (and appropriate parameters); when it wishes to remove an alternative, it does so using update-alternatives --remove. You can use these to provide your own alternatives if necessary.
Note that in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually.
If for some reason an alternative-managed file is not a symlink, update-alternatives will consider that the alternative is broken and will refuse to touch it.
answered Jan 22 at 13:15
Stephen Kitt
142k22308371
The way update-alternatives works is described in its manpage. The list of available alternatives for a given command (or file, in general — alternatives aren’t limited to commands) is stored in a file in /var/lib/dpkg/alternatives on Debian and derivatives; thus the alternatives for java are stored in /var/lib/dpkg/alternatives/java. On Fedora, RHEL, and derivatives, the files are stored in /var/lib/alternatives.
When a package wishes to provide an alternative, it installs it using update-alternatives --install (and appropriate parameters); when it wishes to remove an alternative, it does so using update-alternatives --remove. You can use these to provide your own alternatives if necessary.
Note that in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually.
If for some reason an alternative-managed file is not a symlink, update-alternatives will consider that the alternative is broken and will refuse to touch it.
answered Jan 22 at 13:15
Stephen Kitt
142k22308371
edited Jan 22 at 13:53
answered Jan 22 at 13:15
Stephen Kitt
142k22308371
answered Jan 22 at 13:15
Stephen Kitt
142k22308371
answered Jan 22 at 13:15
Stephen Kitt
142k22308371
142k22308371
Interesting note about java alternatives there. I'm not at all familiar with how or why that would be the case, however usingupdate-alternativeshas always worked for me when dealing with java. Additionally, while the original work was created by debian developers, RedHat-based distros have adapted it as well. Although, there is no specificupdate-java-alternativescommand on RHEL, e.g. It might be worth noting as well, on RedHat-based systems, the path is/var/lib/alternativesfor the alternative scripts.
– ILMostro_7
Jan 22 at 13:48
1
@ILMostro_7 right,update-alternativesstill works,update-java-alternativesmakes it easier to update all the JRE/JDK-provided tools when changing JVMs (look at the/var/lib/jvm/.*.jinfofiles for details). Thanks for the comment, I’ve updated my answer.
– Stephen Kitt
Jan 22 at 13:51
Thanks. Why "in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually" ? I am reading askubuntu.com/questions/159575/…, but still can't figure it out.
– Tim
Jan 22 at 15:28
@Tim, for Java packages, there are lots of different alternatives, none of which are connected (partly because you might only have a sub-selection of the commands installed); so if you want to switch from Java 8 to Java 9 for example, you’d have to update a couple of dozen alternatives manually...update-java-alternativesdoes that for you.
– Stephen Kitt
Jan 22 at 15:30
What are " a couple of dozen alternatives" that I have to update manually? Is$JAVA_HOMEincluded?
– Tim
Jan 22 at 15:39
 |Â
show 7 more comments
Interesting note about java alternatives there. I'm not at all familiar with how or why that would be the case, however usingupdate-alternativeshas always worked for me when dealing with java. Additionally, while the original work was created by debian developers, RedHat-based distros have adapted it as well. Although, there is no specificupdate-java-alternativescommand on RHEL, e.g. It might be worth noting as well, on RedHat-based systems, the path is/var/lib/alternativesfor the alternative scripts.
– ILMostro_7
Jan 22 at 13:48
1
@ILMostro_7 right,update-alternativesstill works,update-java-alternativesmakes it easier to update all the JRE/JDK-provided tools when changing JVMs (look at the/var/lib/jvm/.*.jinfofiles for details). Thanks for the comment, I’ve updated my answer.
– Stephen Kitt
Jan 22 at 13:51
Thanks. Why "in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually" ? I am reading askubuntu.com/questions/159575/…, but still can't figure it out.
– Tim
Jan 22 at 15:28
@Tim, for Java packages, there are lots of different alternatives, none of which are connected (partly because you might only have a sub-selection of the commands installed); so if you want to switch from Java 8 to Java 9 for example, you’d have to update a couple of dozen alternatives manually...update-java-alternativesdoes that for you.
– Stephen Kitt
Jan 22 at 15:30
What are " a couple of dozen alternatives" that I have to update manually? Is$JAVA_HOMEincluded?
– Tim
Jan 22 at 15:39
Interesting note about java alternatives there. I'm not at all familiar with how or why that would be the case, however using
update-alternatives has always worked for me when dealing with java. Additionally, while the original work was created by debian developers, RedHat-based distros have adapted it as well. Although, there is no specific update-java-alternatives command on RHEL, e.g. It might be worth noting as well, on RedHat-based systems, the path is /var/lib/alternatives for the alternative scripts.– ILMostro_7
Jan 22 at 13:48
Interesting note about java alternatives there. I'm not at all familiar with how or why that would be the case, however using
update-alternatives has always worked for me when dealing with java. Additionally, while the original work was created by debian developers, RedHat-based distros have adapted it as well. Although, there is no specific update-java-alternatives command on RHEL, e.g. It might be worth noting as well, on RedHat-based systems, the path is /var/lib/alternatives for the alternative scripts.– ILMostro_7
Jan 22 at 13:48
1
1
@ILMostro_7 right,
update-alternatives still works, update-java-alternatives makes it easier to update all the JRE/JDK-provided tools when changing JVMs (look at the /var/lib/jvm/.*.jinfo files for details). Thanks for the comment, I’ve updated my answer.– Stephen Kitt
Jan 22 at 13:51
@ILMostro_7 right,
update-alternatives still works, update-java-alternatives makes it easier to update all the JRE/JDK-provided tools when changing JVMs (look at the /var/lib/jvm/.*.jinfo files for details). Thanks for the comment, I’ve updated my answer.– Stephen Kitt
Jan 22 at 13:51
Thanks. Why "in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually" ? I am reading askubuntu.com/questions/159575/…, but still can't figure it out.
– Tim
Jan 22 at 15:28
Thanks. Why "in Java’s case specifically, on Debian and derivatives, the alternatives handling is a little more complex and you should use update-java-alternatives instead of manipulating all the alternatives manually" ? I am reading askubuntu.com/questions/159575/…, but still can't figure it out.
– Tim
Jan 22 at 15:28
@Tim, for Java packages, there are lots of different alternatives, none of which are connected (partly because you might only have a sub-selection of the commands installed); so if you want to switch from Java 8 to Java 9 for example, you’d have to update a couple of dozen alternatives manually...
update-java-alternatives does that for you.– Stephen Kitt
Jan 22 at 15:30
@Tim, for Java packages, there are lots of different alternatives, none of which are connected (partly because you might only have a sub-selection of the commands installed); so if you want to switch from Java 8 to Java 9 for example, you’d have to update a couple of dozen alternatives manually...
update-java-alternatives does that for you.– Stephen Kitt
Jan 22 at 15:30
What are " a couple of dozen alternatives" that I have to update manually? Is
$JAVA_HOME included?– Tim
Jan 22 at 15:39
What are " a couple of dozen alternatives" that I have to update manually? Is
$JAVA_HOME included?– Tim
Jan 22 at 15:39
 |Â
show 7 more comments
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1
I usually (ab)use
ltraceandstracefor those quick doubts.– Rui F Ribeiro
Jan 22 at 13:28
Or, list the contents of the package that provides the command/binary, and traverse the directories and read its manpage(s).
– ILMostro_7
Jan 22 at 13:42