fix: prevent false positives in already running k0s instance detection

The main bugfix is to check if a possibly running pid from the runtime
config not only exists as a process, but also is the same excutable
image that is checking.

All platforms use a common library for ps-style checks now in this
implementation.

This changes the behavior for all platforms to use a common library
to perform the "is k0s running" checks on startup. The advantage is,
that the code is much more simple, the disadvantage that an additional
library is now required with additional sub-dependencies.

This commit also refactors the function checkPid into checkInstanceRunning,
since the previous implementation did not allow for more complex error
handling and would have hidden errors. More complex error handling is
now required because the implementation is more complex.

Signed-off-by: Peter Honeder <[email protected]>

go.mod

@@ -83,6 +83,8 @@ require (
 	sigs.k8s.io/yaml v1.4.0
 )
 
+require github.com/shirou/gopsutil/v4 v4.24.12
+
 require (
 	dario.cat/mergo v1.0.1 // indirect
 	github.com/AdaLogics/go-fuzz-headers v0.0.0-20230811130428-ced1acdcaa24 // indirect
@@ -131,6 +133,7 @@ require (
 	github.com/docker/go-metrics v0.0.1 // indirect
 	github.com/docker/go-units v0.5.0 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
+	github.com/ebitengine/purego v0.8.1 // indirect
 	github.com/emicklei/go-restful/v3 v3.11.0 // indirect
 	github.com/evanphx/json-patch/v5 v5.9.0 // indirect
 	github.com/exponent-io/jsonpath v0.0.0-20151013193312-d6023ce2651d // indirect
@@ -143,6 +146,7 @@ require (
 	github.com/go-errors/errors v1.4.2 // indirect
 	github.com/go-gorp/gorp/v3 v3.1.0 // indirect
 	github.com/go-logr/stdr v1.2.2 // indirect
+	github.com/go-ole/go-ole v1.2.6 // indirect
 	github.com/go-openapi/jsonreference v0.20.2 // indirect
 	github.com/go-openapi/swag v0.23.0 // indirect
 	github.com/go-playground/locales v0.14.1 // indirect
@@ -185,6 +189,7 @@ require (
 	github.com/lib/pq v1.10.9 // indirect
 	github.com/liggitt/tabwriter v0.0.0-20181228230101-89fcab3d43de // indirect
 	github.com/lithammer/dedent v1.1.0 // indirect
+	github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0 // indirect
 	github.com/mailru/easyjson v0.7.7 // indirect
 	github.com/mattn/go-colorable v0.1.13 // indirect
 	github.com/mattn/go-isatty v0.0.17 // indirect
@@ -214,6 +219,7 @@ require (
 	github.com/peterbourgon/diskv v2.0.1+incompatible // indirect
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
+	github.com/power-devops/perfstat v0.0.0-20210106213030-5aafc221ea8c // indirect
 	github.com/prometheus/client_golang v1.19.1 // indirect
 	github.com/prometheus/client_model v0.6.1 // indirect
 	github.com/prometheus/common v0.55.0 // indirect
@@ -228,6 +234,8 @@ require (
 	github.com/spf13/cast v1.7.0 // indirect
 	github.com/stoewer/go-strcase v1.2.0 // indirect
 	github.com/stretchr/objx v0.5.2 // indirect
+	github.com/tklauser/go-sysconf v0.3.12 // indirect
+	github.com/tklauser/numcpus v0.6.1 // indirect
 	github.com/vishvananda/netns v0.0.4 // indirect
 	github.com/weppos/publicsuffix-go v0.15.1-0.20210511084619-b1f36a2d6c0b // indirect
 	github.com/x448/float16 v0.8.4 // indirect
@@ -237,6 +245,7 @@ require (
 	github.com/xiang90/probing v0.0.0-20190116061207-43a291ad63a2 // indirect
 	github.com/xlab/treeprint v1.2.0 // indirect
 	github.com/xtgo/uuid v0.0.0-20140804021211-a0b114877d4c // indirect
+	github.com/yusufpapurcu/wmi v1.2.4 // indirect
 	github.com/zmap/zcrypto v0.0.0-20210511125630-18f1e0152cfc // indirect
 	github.com/zmap/zlint/v3 v3.1.0 // indirect
 	go.etcd.io/bbolt v1.3.11 // indirect

go.sum

@@ -158,6 +158,8 @@ github.com/docker/libtrust v0.0.0-20150114040149-fa567046d9b1 h1:ZClxb8laGDf5arX
 github.com/docker/libtrust v0.0.0-20150114040149-fa567046d9b1/go.mod h1:cyGadeNEkKy96OOhEzfZl+yxihPEzKnqJwvfuSUqbZE=
 github.com/dustin/go-humanize v1.0.1 h1:GzkhY7T5VNhEkwH0PVJgjz+fX1rhBrR7pRT3mDkpeCY=
 github.com/dustin/go-humanize v1.0.1/go.mod h1:Mu1zIs6XwVuF/gI1OepvI0qD18qycQx+mFykh5fBlto=
+github.com/ebitengine/purego v0.8.1 h1:sdRKd6plj7KYW33EH5As6YKfe8m9zbN9JMrOjNVF/BE=
+github.com/ebitengine/purego v0.8.1/go.mod h1:iIjxzd6CiRiOG0UyXP+V1+jWqUXVjPKLAI0mRfJZTmQ=
 github.com/emicklei/go-restful/v3 v3.11.0 h1:rAQeMHw1c7zTmncogyy8VvRZwtkmkZ4FxERmMY4rD+g=
 github.com/emicklei/go-restful/v3 v3.11.0/go.mod h1:6n3XBCmQQb25CM2LCACGz8ukIrRry+4bhvbpWn3mrbc=
 github.com/envoyproxy/go-control-plane v0.9.0/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
@@ -205,6 +207,8 @@ github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
 github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
 github.com/go-logr/zapr v1.3.0 h1:XGdV8XW8zdwFiwOA2Dryh1gj2KRQyOOoNmBy4EplIcQ=
 github.com/go-logr/zapr v1.3.0/go.mod h1:YKepepNBd1u/oyhd/yQmtjVXmm9uML4IXUgMOwR8/Gg=
+github.com/go-ole/go-ole v1.2.6 h1:/Fpf6oFPoeFik9ty7siob0G6Ke8QvQEuVcuChpwXzpY=
+github.com/go-ole/go-ole v1.2.6/go.mod h1:pprOEPIfldk/42T2oK7lQ4v4JSDwmV0As9GaiUsvbm0=
 github.com/go-openapi/jsonpointer v0.19.6/go.mod h1:osyAmYz/mB/C3I+WsTTSgw1ONzaLJoLCyoi6/zppojs=
 github.com/go-openapi/jsonpointer v0.21.0 h1:YgdVicSA9vH5RiHs9TZW5oyafXZFc6+2Vc1rr/O9oNQ=
 github.com/go-openapi/jsonpointer v0.21.0/go.mod h1:IUyH9l/+uyhIYQ/PXVA41Rexl+kOkAPDdXEYns6fzUY=
@@ -283,6 +287,7 @@ github.com/google/go-cmp v0.5.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/
 github.com/google/go-cmp v0.5.1/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.5.3/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/google/go-cmp v0.5.6/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
 github.com/google/go-cmp v0.5.9/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
 github.com/google/go-cmp v0.6.0 h1:ofyhxvXcZhMsU5ulbFiLKl/XBFqE1GSq7atu8tAmTRI=
 github.com/google/go-cmp v0.6.0/go.mod h1:17dUlkBOakJ0+DkrSSNjCkIjxS6bF9zb3elmeNGIjoY=
@@ -389,6 +394,8 @@ github.com/lithammer/dedent v1.1.0 h1:VNzHMVCBNG1j0fh3OrsFRkVUwStdDArbgBWoPAffkt
 github.com/lithammer/dedent v1.1.0/go.mod h1:jrXYCQtgg0nJiN+StA2KgR7w6CiQNv9Fd/Z9BP0jIOc=
 github.com/logrusorgru/aurora/v3 v3.0.0 h1:R6zcoZZbvVcGMvDCKo45A9U/lzYyzl5NfYIvznmDfE4=
 github.com/logrusorgru/aurora/v3 v3.0.0/go.mod h1:vsR12bk5grlLvLXAYrBsb5Oc/N+LxAlxggSjiwMnCUc=
+github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0 h1:6E+4a0GO5zZEnZ81pIr0yLvtUWk2if982qA3F3QD6H4=
+github.com/lufia/plan9stats v0.0.0-20211012122336-39d0f177ccd0/go.mod h1:zJYVVT2jmtg6P3p1VtQj7WsuWi/y4VnjVBn7F8KPB3I=
 github.com/mailru/easyjson v0.7.7 h1:UGYAvKxe3sBsEDzO8ZeWOSlIQfWFlxbzLZe7hwFURr0=
 github.com/mailru/easyjson v0.7.7/go.mod h1:xzfreul335JAWq5oZzymOObrkdz5UnU4kGfJJLY9Nlc=
 github.com/mattn/go-colorable v0.1.2/go.mod h1:U0ppj6V5qS13XJ6of8GYAs25YV2eR4EVcfRqFIhoBtE=
@@ -500,6 +507,8 @@ github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINE
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 h1:Jamvg5psRIccs7FGNTlIRMkT8wgtp5eCXdBlqhYGL6U=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/power-devops/perfstat v0.0.0-20210106213030-5aafc221ea8c h1:ncq/mPwQF4JjgDlrVEn3C11VoGHZN7m8qihwgMEtzYw=
+github.com/power-devops/perfstat v0.0.0-20210106213030-5aafc221ea8c/go.mod h1:OmDBASR4679mdNQnz2pUhc2G8CO2JrUAVFDRBDP/hJE=
 github.com/poy/onpar v1.1.2 h1:QaNrNiZx0+Nar5dLgTVp5mXkyoVFIbepjyEoGSnhbAY=
 github.com/poy/onpar v1.1.2/go.mod h1:6X8FLNoxyr9kkmnlqpK6LSoiOtrO6MICtWwEuWkLjzg=
 github.com/prometheus/client_golang v0.9.1/go.mod h1:7SWBe2y4D6OKWSNQJUaRYU/AaXPKyh/dDVn+NZz0KFw=
@@ -543,6 +552,8 @@ github.com/segmentio/backo-go v0.0.0-20200129164019-23eae7c10bd3 h1:ZuhckGJ10ula
 github.com/segmentio/backo-go v0.0.0-20200129164019-23eae7c10bd3/go.mod h1:9/Rh6yILuLysoQnZ2oNooD2g7aBnvM7r/fNVxRNWfBc=
 github.com/sergi/go-diff v1.2.0 h1:XU+rvMAioB0UC3q1MFrIQy4Vo5/4VsRDQQXHsEya6xQ=
 github.com/sergi/go-diff v1.2.0/go.mod h1:STckp+ISIX8hZLjrqAeVduY0gWCT9IjLuqbuNXdaHfM=
+github.com/shirou/gopsutil/v4 v4.24.12 h1:qvePBOk20e0IKA1QXrIIU+jmk+zEiYVVx06WjBRlZo4=
+github.com/shirou/gopsutil/v4 v4.24.12/go.mod h1:DCtMPAad2XceTeIAbGyVfycbYQNBGk2P8cvDi7/VN9o=
 github.com/shopspring/decimal v1.4.0 h1:bxl37RwXBklmTi0C79JfXCEBD1cqqHt0bbgBAGFp81k=
 github.com/shopspring/decimal v1.4.0/go.mod h1:gawqmDU56v4yIKSwfBSFip1HdCCXN8/+DMd9qYNcwME=
 github.com/sirupsen/logrus v1.2.0/go.mod h1:LxeOpSwHxABJmUn/MG1IvRgCAasNZTLOkJPxbbu5VWo=
@@ -578,6 +589,10 @@ github.com/stretchr/testify v1.8.4/go.mod h1:sz/lmYIOXD/1dqDmKjjqLyZ2RngseejIcXl
 github.com/stretchr/testify v1.9.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
 github.com/stretchr/testify v1.10.0 h1:Xv5erBjTwe/5IxqUQTdXv5kgmIvbHo3QQyRwhJsOfJA=
 github.com/stretchr/testify v1.10.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+github.com/tklauser/go-sysconf v0.3.12 h1:0QaGUFOdQaIVdPgfITYzaTegZvdCjmYO52cSFAEVmqU=
+github.com/tklauser/go-sysconf v0.3.12/go.mod h1:Ho14jnntGE1fpdOqQEEaiKRpvIavV0hSfmBq8nJbHYI=
+github.com/tklauser/numcpus v0.6.1 h1:ng9scYS7az0Bk4OZLvrNXNSAO2Pxr1XXRAPyjhIx+Fk=
+github.com/tklauser/numcpus v0.6.1/go.mod h1:1XfjsgE2zo8GVw7POkMbHENHzVg3GzmoZ9fESEdAacY=
 github.com/tmc/grpc-websocket-proxy v0.0.0-20220101234140-673ab2c3ae75 h1:6fotK7otjonDflCTK0BCfls4SPy3NcCVb5dqqmbRknE=
 github.com/tmc/grpc-websocket-proxy v0.0.0-20220101234140-673ab2c3ae75/go.mod h1:KO6IkyS8Y3j8OdNO85qEYBsRPuteD+YciPomcXdrMnk=
 github.com/urfave/cli v1.22.16 h1:MH0k6uJxdwdeWQTwhSO42Pwr4YLrNLwBtg1MRgTqPdQ=
@@ -608,6 +623,8 @@ github.com/xtgo/uuid v0.0.0-20140804021211-a0b114877d4c h1:3lbZUMbMiGUW/LMkfsEAB
 github.com/xtgo/uuid v0.0.0-20140804021211-a0b114877d4c/go.mod h1:UrdRz5enIKZ63MEE3IF9l2/ebyx59GyGgPi+tICQdmM=
 github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
+github.com/yusufpapurcu/wmi v1.2.4 h1:zFUKzehAFReQwLys1b/iSMl+JQGSCSjtVqQn9bBrPo0=
+github.com/yusufpapurcu/wmi v1.2.4/go.mod h1:SBZ9tNy3G9/m5Oi98Zks0QjeHVDvuK0qfxQmPyzfmi0=
 github.com/yvasiyarov/go-metrics v0.0.0-20140926110328-57bccd1ccd43 h1:+lm10QQTNSBd8DVTNGHx7o/IKu9HYDvLMffDhbyLccI=
 github.com/yvasiyarov/go-metrics v0.0.0-20140926110328-57bccd1ccd43/go.mod h1:aX5oPXxHm3bOH+xeAttToC8pqch2ScQN/JoXYupl6xs=
 github.com/yvasiyarov/gorelic v0.0.0-20141212073537-a9bba5b9ab50 h1:hlE8//ciYMztlGpl/VA+Zm1AcTPHYkHJPbHqE6WJUXE=
@@ -725,6 +742,7 @@ golang.org/x/sys v0.0.0-20190222072716-a9d3bda3a223/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20190412213103-97732733099d/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190801041406-cbf593c0f2f3/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20190904154756-749cb33beabd/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20190916202348-b4ddaad3f8a3/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191005200804-aed5e4c7ecf9/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191026070338-33540a1f6037/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20191120155948-bd437916bb0e/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
@@ -734,6 +752,7 @@ golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7w
 golang.org/x/sys v0.0.0-20201015000850-e3ed0017c211/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20201126233918-771906719818/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20201204225414-ed752295db88/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210112080510-489259a85091/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
@@ -744,7 +763,9 @@ golang.org/x/sys v0.0.0-20220715151400-c0bba94af5f8/go.mod h1:oPkhp1MJrh7nUepCBc
 golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.1.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.2.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.8.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.10.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.11.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.28.0 h1:Fksou7UEQUWlKvIdsqzJmUmCX3cZuD2+P3XyyzwMhlA=
 golang.org/x/sys v0.28.0/go.mod h1:/VUhepiaJMQUp4+oa/7Zr1D23ma6VTLIYjOOTFZPUcA=
 golang.org/x/term v0.0.0-20201117132131-f5c789dd3221/go.mod h1:Nr5EML6q2oocZ2LXRh80K7BxOlk5/8JxuGnuhpl+muw=

pkg/config/runtime.go

@@ -28,6 +28,7 @@ import (
 	"github.com/k0sproject/k0s/internal/pkg/dir"
 	"github.com/k0sproject/k0s/pkg/apis/k0s/v1beta1"
 	"github.com/k0sproject/k0s/pkg/constant"
+	"github.com/shirou/gopsutil/v4/process"
 
 	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
 
@@ -97,9 +98,14 @@ func LoadRuntimeConfig(k0sVars *CfgVars) (*RuntimeConfigSpec, error) {
 	// an error is returned, which allows the controller startup to proceed to
 	// initialize a new runtime config.
 	if spec.Pid != 0 {
-		if err := checkPid(spec.Pid); err != nil {
+		isRunning, err := checkInstanceRunning(spec.Pid)
+		if !isRunning || err != nil {
 			defer func() { _ = spec.Cleanup() }()
-			return nil, errors.Join(ErrK0sNotRunning, err)
+			if !isRunning {
+				return nil, errors.Join(ErrK0sNotRunning, err)
+			} else if err != nil {
+				return nil, fmt.Errorf("%w: failed to check if instance is running", err)
+			}
 		}
 	}
 
@@ -192,3 +198,58 @@ func (r *RuntimeConfigSpec) Cleanup() error {
 	}
 	return nil
 }
+
+// returns:
+// - true, nil if the pid is the same k0s executable and running
+// - false, nil if the pid is not running or another executable
+// - false, error on any kind of internal error checking the status
+//
+// process does not exist -> error
+// process exists and is same executable -> error
+// process exists and is not same executable -> nil
+func checkInstanceRunning(pid int) (bool, error) {
+	// create the process object
+	proc, err := process.NewProcess(int32(pid))
+	if err != nil {
+		return false, fmt.Errorf("failed to create process object: %w", err)
+	}
+
+	// first check if the pid is running
+	isRunning, err := proc.IsRunning()
+	if err != nil {
+		return false, fmt.Errorf("failed to check if process is running: %w", err)
+	}
+	if !isRunning {
+		return false, nil
+	}
+
+	// Get the executable path of the target pid
+	// - no need to resolve symlinks here, it is already a resolved path
+	exeTarget, err := proc.Exe()
+	if err != nil {
+		return false, fmt.Errorf("failed to get process executable path: %w", err)
+	}
+
+	// Get the executable path of the current process
+	currentExe, err := os.Executable()
+	if err != nil {
+		return false, fmt.Errorf("failed to get current executable: %w", err)
+	}
+	fmt.Println("before symlink resolve: ", currentExe)
+
+	// Resolve symlinks
+	currentExe, err = filepath.EvalSymlinks(currentExe)
+	if err != nil {
+		return false, fmt.Errorf("failed to resolve current executable symlinks: %w", err)
+	}
+	fmt.Println("currentExe: ", currentExe, "exeTarget: ", exeTarget)
+
+	// check that the executable is the same in order to issue an error, if it would be a different
+	// than it can't be a running instance of k0s, which the check is all about
+	if exeTarget != currentExe {
+		return false, nil
+	}
+
+	// return that k0s is running witht he same executable image
+	return true, nil
+}

pkg/config/runtime_test.go

@@ -21,7 +21,10 @@ import (
 	"testing"
 
 	"github.com/k0sproject/k0s/pkg/apis/k0s/v1beta1"
+	"github.com/shirou/gopsutil/v4/process"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"sigs.k8s.io/yaml"
 )
 
 func TestLoadRuntimeConfig_Legacy(t *testing.T) {
@@ -86,6 +89,12 @@ spec:
 	assert.ErrorIs(t, err, ErrK0sNotRunning)
 }
 
+// The idea behind this test is:
+// - test to create a new runtime config from scratch
+// - actually test if k0s is still running by checking against:
+//   - the same executable with the same pid as the runtime config
+//   - a different executable with the same pid as the runtime config
+//   - a pid that is not running anymore
 func TestNewRuntimeConfig(t *testing.T) {
 	// create a temporary directory for k0s files
 	tempDir, err := os.MkdirTemp("", "k0s")
@@ -110,6 +119,7 @@ func TestNewRuntimeConfig(t *testing.T) {
 	}
 
 	// create a new runtime config and check if it's valid
+	// this will set the pid property to the current process id of the test run
 	spec, err := NewRuntimeConfig(k0sVars)
 	assert.NoError(t, err)
 	assert.NotNil(t, spec)
@@ -121,7 +131,94 @@ func TestNewRuntimeConfig(t *testing.T) {
 	assert.Equal(t, "10.0.0.1", cfg.Spec.API.Address)
 
 	// try to create a new runtime config when one is already active and check if it returns an error
+	// this will fail with ErrK0sAlreadyRunning since the pid property is this currently
+	// executing test process (with the unit test)
 	_, err = NewRuntimeConfig(k0sVars)
 	assert.Error(t, err)
 	assert.ErrorIs(t, err, ErrK0sAlreadyRunning)
+
+	// Start a process in the background with a shell that sleeps for a long time
+	// (infinity is not available on default macOS zsh), this simulates
+	// a different running process with the same pid as stored in the runtime config, but
+	// from a different executable image
+	cmd := getBackgroundCommand()
+	err = cmd.Start()
+	require.NoError(t, err, "Failed to start process")
+
+	// remember the newly started PID
+	pid := cmd.Process.Pid
+	cleanupPid := pid
+
+	// create the process object
+	proc, err := process.NewProcess(int32(pid))
+	require.NoError(t, err, "failed to create process object")
+
+	// check that the pid is running
+	isRunning, err := proc.IsRunning()
+	require.NoError(t, err, "IsRunning works correctly for newly started background process")
+	require.True(t, isRunning, "background process is running")
+
+	// this is the cleanup function that cleans the process in case of a test failure
+	cleanupFunc := func() {
+		if cleanupPid != 0 {
+			// Shut down the child process (killing it is fine here)
+			err = proc.Kill()
+			require.NoError(t, err, "Failed to shut down child process")
+
+			// Wait for the command to exit (ingore the error, since we're just cleaning up)
+			cmd.Wait()
+
+			// set the cleanupPid to 0 to indicate successful termination and not clean up twice
+			cleanupPid = 0
+		}
+	}
+	defer cleanupFunc()
+
+	// modify the pid in the runtime config
+	err = updateRuntimeConfigPID(k0sVars.RuntimeConfigPath, pid)
+	require.NoError(t, err)
+
+	// create a new runtime config, but this time with a pid of a process that actually exists
+	// but is from a different executable image
+	_, err = NewRuntimeConfig(k0sVars)
+	require.NoError(t, err)
+
+	// now kill the other process in order to test for the same pid, with the difference
+	// that we now know it's from a process that is definitely not running anymore
+	cleanupFunc()
+
+	// modify the pid in the runtime config (again to the same pid, which is not running anymore)
+	// this needs to be done since the previous PID value was overwritten with the new
+	// config from the last call to NewRuntimeConfig)
+	err = updateRuntimeConfigPID(k0sVars.RuntimeConfigPath, pid)
+	require.NoError(t, err)
+
+	// create a new runtime config, this should also succeed since the pid is not running
+	_, err = NewRuntimeConfig(k0sVars)
+	assert.NoError(t, err)
+}
+
+func updateRuntimeConfigPID(path string, pid int) error {
+	content, err := os.ReadFile(path)
+	if err != nil {
+		return err
+	}
+
+	config := &RuntimeConfig{}
+	err = yaml.Unmarshal(content, config)
+	if err != nil {
+		return err
+	}
+	config.Spec.Pid = pid
+
+	content, err = yaml.Marshal(config)
+	if err != nil {
+		return err
+	}
+
+	err = os.WriteFile(path, content, 0600)
+	if err != nil {
+		return err
+	}
+	return nil
 }