update-alternativesの使い方

システムで使われるプログラムのバージョン管理を行うためのupdate-alternativesの使い方。

確認

# update-alternatives --display java
java - manual mode
  link currently points to /usr/lib/jvm/default-java/bin/java
/usr/lib/jvm/default-java/bin/java - priority 1
/usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java - priority 1061
  slave java.1.gz: /usr/lib/jvm/java-6-openjdk-amd64/jre/man/man1/java.1.gz
/usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java - priority 1051
  slave java.1.gz: /usr/lib/jvm/java-7-openjdk-amd64/jre/man/man1/java.1.gz
/usr/lib/jvm/java-8-oracle/jre/bin/java - priority 1062
  slave java.1.gz: /usr/lib/jvm/java-8-oracle/man/man1/java.1.gz
Current 'best' version is '/usr/lib/jvm/java-8-oracle/jre/bin/java'.

変更

# update-alternatives --config java
There are 4 choices for the alternative java (providing /usr/bin/java).

  Selection    Path                                            Priority   Status
------------------------------------------------------------
  0            /usr/lib/jvm/java-8-oracle/jre/bin/java          1062      auto mode
* 1            /usr/lib/jvm/default-java/bin/java               1         manual mode
  2            /usr/lib/jvm/java-6-openjdk-amd64/jre/bin/java   1061      manual mode
  3            /usr/lib/jvm/java-7-openjdk-amd64/jre/bin/java   1051      manual mode
  4            /usr/lib/jvm/java-8-oracle/jre/bin/java          1062      manual mode

Press enter to keep the current choice[*], or type selection number: 1

autoモード

プライオリティ値で自動的に使うものを選択するautoモードへの切り替え

# update-alternatives --auto vi

まずマニュアルで2番を選択してみる

# update-alternatives --config vi
There are 2 choices for the alternative vi (providing /usr/bin/vi).

  Selection    Path                Priority   Status
------------------------------------------------------------
  0            /usr/bin/vim.basic   30        auto mode
  1            /usr/bin/vim.basic   30        manual mode
* 2            /usr/bin/vim.tiny    10        manual mode

Press enter to keep the current choice[*], or type selection number: 
root@stg-jenkins-n01:/usr/bin# update-alternatives --auto vi
update-alternatives: using /usr/bin/vim.basic to provide /usr/bin/vi (vi) in auto mode.

その後autoモードにすると、priortyで選ばれているのがわかる

# update-alternatives --config vi
There are 2 choices for the alternative vi (providing /usr/bin/vi).

  Selection    Path                Priority   Status
------------------------------------------------------------
* 0            /usr/bin/vim.basic   30        auto mode
  1            /usr/bin/vim.basic   30        manual mode
  2            /usr/bin/vim.tiny    10        manual mode